Where did all the walleye go?

By Larry Jones © 2016


Larry Jones came to Bobcaygeon in 1955 as a young teenager. He worked for the Department of Lands and Forests at the Muskellunge Research Station on Nogie’s Creek. This position was a good fit to his real passion, which was taxidermy. This was something that caught his imagination as a 10-year-old. Larry soon established a reputation for his excellent work; not only the direct work with the animals, fish, and birds, but also for the complete montage which was worthy of any natural history museum. He has enjoyed a long career as a taxidermist in Bobcaygeon, during which time he won many awards for his extraordinary skill. Larry is also a keen fisherman with many tournament successes. He has lived close to nature for his entire life, and is a keen observer of the changes that have occurred as Bobcaygeon expanded. He has also been a member of numerous committees who have discussed these changes.


In the 1970s these changes started to have a serious impact on the local ecology. This was most severe on the fish stocks, the bird populations, and the overall health of the lake system known as the Trent-Severn. Larry formed a hypothesis based on the introduction of the new bottom discharge dams. That theory is the subject of this article. The death of the lakes has also been one of my major concerns since I came here in 1993. Therefore, I was delighted when Larry asked me to help organize his material into a publishable form. I have been his amanuensis. This has involved some research on the internet to find supporting material. That material has been reproduced here in italics. There seemed to be no point in rewriting this material because, in essence, it represents the widely held opinions of the scientific community. But, on the whole, I have worked with his material, and listened to him explain his theory in some detail. This is Larry’s story. Let us all listen carefully; and then take action.

How it used to be

How it used to be

In the beginning the water ran eastward from the high point of Balsam Lake to its outlet at Trenton, on the St. Lawrence. Another outlet from Balsam Lakes sent the water westwards to pour into Lake Simcoe. This waterway from the St. Lawrence to Lake Simcoe, and onward to the Great Lakes, was the highway for the indigenous people. It is the path they took with Champlain, and other early explorers, as the traders arrived from Europe. The water ran down through lakes, marshes, and rivers. It skittered over the numerous rapids, and plunged over the waterfalls. The water was packed with dissolved oxygen, which provided an ideal habitat for Lake Herring (Cisco), White Suckers, and other native fish.


In the spring the snow melt turned the waterway into raging torrents. This flushed out debris, and silt. The water bubbled furiously over the beds of small rocks that are vital breeding grounds for some fish. This was a happy time for the environment, and for all its creatures; including Man. The arrival of the ‘white man’ changed all that. A waterway that involves portages, and white-water rapids, is a challenge to moving trade goods, logs from the early lumber mills, and the household goods of the early settlers. Thus began the era of dam building.


These first dams had sluice gates to control the water flow. It was a simple device using logs. The top log determined the upstream water level. The logs could be lifted up to increase the flow rate, or lowered down to decrease the rate. It is significant, and, as we will see later, very significant that the water flowed over the top of the dam. River water does not flow at a uniform rate across its width, and depth. The water close to the banks, or close to the bottom, moves very slowly. The fastest water flows at the surface, mid-stream. The log dams did not stop this surface flow to any major degree. Oxygen enters water largely through the interaction of the air with a water surface. This effect is increased enormously in rapids, waterfalls, and during stormy conditions.]


The impact of civilization, the logging trade, and the dams, was certainly bad for the environment, especially the aquatic environment. However, it was not catastrophic. Lake herrings, and suckers, were still so numerous that they were caught in huge numbers, to be used as fertilizer on the new fields. However, these fish are not relished as human food. Between 1921 and 1940, walleye were introduced to the lakes, mainly because they are an excellent table fish. These fish have the same habitat requirements as white suckers; namely fast moving water, with a high oxygen content, flushing over the small rocks that make up an ideal spawning ground. The walleye thrived extremely well. Soon Pigeon Lake, and the other lakes along what was now the Trent-Severn waterway, were brimming with walleye.


During the spawning season the number of walleyes, and suckers, was so large that the smell of fish would drift into the towns. Bobcaygeon, and the other small towns along the waterway, became fishing meccas. Fishing lodge records show that almost half the guest were Americans. This was a boom time. Fishing guides were in great demand, tackle shops were prosperous, even taxidermists experienced a steady demand for their expertise.


Shad flies, or Mayflies, beloved of all manner of fish, rose in clouds so dense that it was difficult to see. It was noted that some cars could not brake properly because their tires would skid on the corpses of the flies. Here again it is very significant that the larval, and emergent stages of many insect, also need fast running, highly oxygenated water. It seems that Mother Nature looks after its creatures in a very rational way.

1970s: the walleye fishery starts to collapse

Few things change rapidly in a large watershed.

The life span of walleye is a decade or more. Even a serious change in the spawning habitat, with a consequent reduction in the juvenile survival rates, would take several years to become noticeable. However, a steady change did begin in the late 70s, and increased in subsequent years. This became noticeable to fishermen in the late 80s. The number of walleye decreased year by year. The American fishermen became increasingly frustrated by the size of their catches. The once flourishing tourist trade collapsed. Another change was also occurring, but went largely unnoticed.

The white suckers were also in decline at the same rate as the walleye. Local fishermen began to ask questions of the provincial government agencies, and of the Trent-Severn Waterways commission. The provincial authorities took a lukewarm interest at their usual glacial pace. And, in characteristic fashion, they set up commissions to look into the matter. The Ministry of Natural Resources was quick to blame overfishing. This was clearly not the case. White suckers are not a popular food fish. They may be caught from time to time, but they do not experience much fishing pressure; certainly nothing comparable to the walleye. However, the white suckers were also disappearing at the same rate as the walleye. It was noted earlier that walleye, and white suckers, occupy the same habitat. This should have alerted the Ministry to a possible habitat problem; but it did not.

When the fishermen tourists left, the expected bounce back in fish numbers did not occur. Since that time the regulations on catch limits, and slot sizes, have become draconian. In practice walleye is now a critically protected species. Even these stern measures have not produced any noticeable change. In recent years the only pleasure in fishing is being out on the lake, not in catching fish.

The next explanation centered on the arrival of Zebra mussels. These occurred long after the damage had been done.

Much has been made of the increase in weeds in the lake. They have become a serious problem for water sports of all kinds. This also decreases the appeal of the Kawarthas as a tourist destination. However, most weeds are beneficial to fish, but an overabundance certainly is not.

Over the years several serious biologists have looked into this problem. They are all looking for a cause, and effect, relationship. So far they have been unsuccessful. Larry Jones, a local taxidermist, outdoorsman, and ecologist, came to the inescapable conclusion that there must be a cause, and effect, relationship – but that the experts had missed the cause. Mr. Jones asked the key question. “What else was happening during the decline period?”

There were some topographical changes. Swamp areas were being drained. Cottage development was happening along miles of shoreline. There were more pleasure craft during the summer months. The nutrient rich runoff from farmers’ fields, road surfaces, the sewage treatment plant, and cottages, was certainly encouraging aquatic weed growth, and the deterioration in water quality. But was this enough to explain the sharp decline in walleye numbers? He felt not. This was an opinion based upon his personal, and expert, knowledge of the walleye life cycle. 


The hydraulic dams are to blame

Larry noticed that about 1969 Trent-Severn began a program of dam upgrades. The log dams were replaced, bit by bit, with bottom discharge dams. Larry began to investigate the consequences of this new system. The following deductions from that hypothesis are self-evident. They require nothing more than common sense, together with a rudimentary knowledge of the subject:

1. Moving bodies of water, such as rivers, reach a uniform temperature. This is why we stir a cup of coffee after adding the cream. 

2. This uniform temperature rises, and then falls, as we move through the four seasons. Many macroinvertebrates depend on this regular cycle of temperature changes throughout the year. It is the biological clock that controls the various stages of their metamorphoses.

3. The top layer of water upstream of a dam is essentially stagnant. This layer heats up much more that the similar layer in a moving river. The density of water decreases as the temperature rises. This, in turn, creates an abnormally steep thermocline in the water body upstream of dams.


4. These regions of warm, still, nutrient rich water are ideal for the growth of algae. The result is increased turbidity, with ever greater absorption of the heat from the sun. The overnight respiration of suspended algae leads to a decrease in dissolved oxygen concentrations in the upper layer – the epilimnion.

5. The lowest layers of water slide along under this static warm upper layer. Thus the cold, deep, layers are in constant contact with the decaying vegetation on the bottom. Decay uses up oxygen from the water in this lowest level – the hypolimnion. The construction of bottom discharge dams has depleted the oxygen concentrations at both the surface, and deep layers.

6. The annual raging torrents caused by spring melt waters are no more.

This annual event was like a fire hose clearing out a drain. The result is the accumulation of decayed matter, and silt, especially in the marshes. This environment is now suitable for the growth of charra. It can completely take over a marshland; where it reduces the available fish habitat. It also clogs intakes used for irrigation, makes swimming or boating difficult, and reduces the aesthetic appeal of our lakes. The silty bottom is now a problem for native plants such as vallisneria (eelgrass), and elodeas, that need to be firmly anchored. They have difficulty in getting their roots down through the silt into the firm bottom. This new balance of nature is clearly evident in the Bobcaygeon area.


7. The water at the bottom of the waterway is much colder than the surface; by as much as 20C.

When this very cold water pours out below the dam the biothermal clock in (2) is sabotaged. The water in the river is now colder than it should be. Many macroinvertebrates depend on a regular cycle of temperatures throughout the year. When we change that, we compromise their survival. For instance, a stonefly may feel the cold temperatures, and delay its metamorphosis. This may mean that at a critical stage in its life it will be living in the depth of winter rather than in autumn, as it should have been. Fish who live on these stone flies, shad flies, and others, are now starved out of existence.


8. Water pressure increases with depth.

This also means that water escaping through a hole at the bottom of a dam, moves faster than through a hole at the top. The cold stream of water from a bottom discharge dam rushes into the calmer ‘pond’ below the dam. This creates a Venturi effect; similar to the air passing over an airplane wing. The lower pressure near the stream makes the water in the pond flow upstream in a semicircular path. This creates a selfperpetuating region of cold, oxygen depleted water, immediately below the dam. That is the very place where fish would spawn, and the macroinvertebrates would flourish. 



Larry built a working model of a dam. He placed some coloured oil on the surface, whereupon this Venturi pattern was easy to see. The model is now with Kawartha Conservation.


9. In a natural waterway there are frequent small floods. However, the managers of the dams on the Trent Severn release large volumes of water, but less frequently. This usually occurs at the time of the spring run-off, or after periods of widespread heavy rains. This process leads to scouring, and armoring, of the riverbed. The higher energy of the sudden floods picks up, and removes, smaller sediments like silt, sand, and gravel; as well as aquatic plants and animals, leafy debris, and large woody debris.

Complex sets of habitats are erased.

The riverbed below the dam becomes like a pavement of cobbles, and loses its value as habitat for plants, macroinvertebrates, and fish.

An excellent example of this effect is seen below the Bobcaygeon dam at drawdown. 


10. The natural flow of water, under normal circumstances, occurs at the surface. The bottom discharge dams create a completely alien environment in which cold, dense, anoxic water, is moving close to the bottom. Walleye require very specific temperatures at various periods in their developmental cycle. These temperatures are critical to their survival. Temperatures should not exceed 10C for egg, and sperm, maturation. Temperatures should then rise quickly up to 15C for greatest hatching success. This should be followed by summer temperatures between 16C, and 27C to maximize their growth rate. It seems likely that the bottom discharge water has a temperature lower than the 9C required for hatching success. This cold water continues to circulate in the basin below the dam due to the Venturi effect.

It is unlikely that this water will warm up in time for a successful hatch. Conversely, the warmer surface water spraying over the top of a dam on a warm spring day, could well reach that temperature. This topsy turvy aquatic environment must, on logical grounds alone, disrupt the ecosystem. In the marshes there may be impacts on turtles, and other amphibians, that have not yet been detected.

11. The Trent-Severn has another problem that could be easily resolved. The water level is lowered considerably – the draw down – as winter approaches. This makes our already shallow lakes even more so. The fish have to move into deeper ‘holes’. The oxygen levels are so low in these holes that many fish do not survive.

This is the well-known ‘winter kill’ effect. Shallow lakes with large amounts of aquatic vegetation, and mucky bottoms, are prone to this problem. They have a much lower oxygen capacity. When this is combined with decaying plants that consume the ‘bank account’ of oxygen that is left, we reach a point where some fish cannot survive.

Winter kill,” and water level fluctuations are dealt with in sections 5.2.3, and 5.2.4 in the Kawartha Lakes Walleye Fishery Review. These issues were clearly a matter of serious concern for the review panel. The review team discounted these drawdowns as being relatively unimportant because the walleye lay their eggs later in the season.

However, the Mayfly nymphs spend various lengths of time, up to two years, foraging on the bottom before emerging as an adult fly. It can be seen at Bobcaygeon that much of their habitat is high and dry from mid-November. This destroys a critical food source for young walleye. Mayfly is a particularly important food source for walleye fry. The calorific value of mayfly is higher than their other major food source, the amphipods. A late arriving prey population, such as the mayfly hatch, results in more predation, and cannibalism, on walleye fry. This problem is reduced when the ecosystem provides abundant forage for all fish. There has been no study to gauge the impact of drawdowns on fish populations. It would be difficult to persuade people to put up with annual flooding of their lakeshore properties, in order to carry out a controlled experiment for ten years, or so. This is probably why it has not been done so far.

12. The previous environmental impacts, taken in their totality, have caused the towns along the Trent-Severn to lose the equivalent of multi-million-dollar fish hatcheries. They have also lost the income from a thriving recreational fishing industry.


The Action Plan

The data firmly supports the assertion that bottom discharge dam gates have had a devastating impact on a formerly healthy waterway. The taxpayers contribute millions of dollars each year to various ministries, conservation authorities, and other ecological groups.

It is worrisome that:

(a) They had not discovered this cause, and effect, relationship revealed by Larry Jones.

(b) Mr. Jones has met numerous times with the experts, and the appropriate authorities. They meetings have all proved fruitless.


The solution to the problem is obvious:

The bottom discharge dams should be replaced with controlled spillways.

This is possible at Bobcaygeon since the older spillways are still in place. Controlled spillways come in a large array of configurations. Some have long discharge chutes that maximizes the contact between the air, and water, with a large increase in the oxygen concentration.

A simple hinged crest gate spillway is shown in the diagram:

 The change to controlled spillways may take some time. However, we could get a head start in Bobcaygeon. The water volume flowing through the dam has a minimum value, even under the driest conditions. This volume could, at all times, be sent over the top of the existing ‘log’ dams. The water in excess of this amount would be controlled as at present. This would have a beneficial effect on the downstream side. Whether, or not, this would be sufficient to significantly improve the fish habitat, could be determined by a monitoring program. The problem we face in the Trent-Severn waterway is not unique. It is an unfortunate result of human expansion, and a mania for controlling the elements.

Some organizations, such as that around Lake Istokpoga, Florida, have accepted this reality. They do not shy away from using every human device to help their lakes back to robust good health. They scraped 1308 acres of silt from along the 21 mile shoreline. This nutrient-rich mud has greatly improved the local farmlands. Two years later (2003), beds of eel grass, and other desirable aquatic plants, were becoming establish. By 2013 the lake had become young again, with excellent fishing. Its nickname became “lunker locker” This problem is well documented on the internet. In this article the material in italics is a direct re-composition of material from expert sources. These internet documents strongly support the evidence presented in this article. The references can be supplied.


The World Wildlife Federation comments that:

We promote sustainable dam projects in certain areas, and encourage an understanding of all the positive and negative impacts of specific dams before their construction and operation.

There is no evidence that shows that this was done for the dams on the Trent Severn.


In summary we find that the evidence suggest that two major causes can satisfactorily explain the decline of the walleye fishery:

1) The first is the annual drawdown.

2) The second is the impact of the bottom discharge dams.


Recent studies mentioned in the review show a stable situation. It is argued, on that basis, that there is no problem. However, these studies were made in the period after the sharp decline. At that point the lakes had established a new equilibrium, and no significant year over year changes are expected. But this new level of stability cannot be compared to the abundance prior to the new dams.

The reviews, and comparisons with other watersheds, looked at many possible causes of the walleye decline. But none considered the impact of bottom discharge dams. We will never return to the ideal situation with the rivers, and lakes, back in their original natural state. But we could move in that direction with some vigor, and financial support.

We all talk ecology. Here is a chance to do it.


Note 1: The swallows are gone too

The shad flies, and other insects, decreased as rapidly as the walleye, and white sucker. This may seem a blessing to some people. But note that the huge flocks of swallows have also gone. Those beautiful birds skimmed the lake surface in large numbers every evening, twittering to each other excitedly. Being on the lake at that time was an exhilarating privilege. This was low flying, but still it “touched the face of god.” The destruction of the important insect habitat may well be an indirect, and unforeseen, consequence of bottom discharge dams.

Note 2: Walleye restocking

Bud Thompson, Reeve of Bobcaygeon, formed a committee to look into this situation. This group felt that a walleye restocking program might solve the problem. The Ministry of Natural Resources wanted a broad study done to show that restocking was a viable option. Data was collected, and several hypotheses were voiced. This material was set out in a Review document, published in October 1994.

Unfortunately, no further action of a practical nature was taken. 

Note 3: Ice fishing 

Ice fishing was banned for about 100 years. In 2007 this regulation was changed to permit ice fishing for pan fish. Unfortunately, the bait does not discriminate between various fish species. It happens that some walleyes are caught. These walleyes are supposed to be returned to the lake quickly, and in good condition. In reality some die, and some find their way to the dinner table. In practice the MNR is unable to rigorously enforce this regulation. It would require more officers than they have available. The net result is that the fragile walleye population experiences an additional stress as it deals with massive environmental changes.

girl fishing on a dock

By Larry Jones © 2016
Research and dictation by Peter Weygang. 

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