Low dissolved oxygen levels affecting trout at Taneycomo

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BRANSON, Mo. – Trout problems at Shepherd of the Hills Hatchery have grabbed recent headlines, but water-quality issues similar to what's occurring at the hatchery are having impacts on Lake Taneycomo, too

Anglers and other visitors to this popular southwest Missouri reservoir were noticing dead trout and, in some cases, foul odors on the upper end of the lake for several weeks, even before conditions at the hatchery became dire. The main reason for Taneycomo's issues is low levels of dissolved oxygen (DO) in the water. The root cause of these DO problems can be traced to summer rains that caused sudden inflows into Table Rock Lake – the primary source of Taneycomo's water. Cooler temperatures should fix the situation. In the meantime, people who fish Taneycomo can help reduce this problem by minimizing the time they take to reel in and release fish.

Anglers can help reduce trout mortality by giving special attention to how they handle trout they catch. Land trout as quick as possible. Extended fights stress fish at any time of year, but can be lethal during times of low DO. Also, minimize the time spent netting and unhooking the fish. Finally, when the fish is unhooked, gently hold it under water until it gains equilibrium and can swim off on its own.

Anglers wishing to report dead fish on Taneycomo can call Missouri Department of Conservation (MDC) Fisheries Management Biologist Shane Bush at Shepherd of the Hills Fish Hatchery, 417-334-4859 or they can call MDC's Southwest Regional Office in Springfield at 417-895-6880.

Blaming summer rains at Table Rock for dead trout in November at Taneycomo may seem like a stretch, but it provides insight into the annual water cycle at both reservoirs and also shows how the two lakes are connected.

Cold water released into Taneycomo from the depths of Table Rock allows trout to thrive in the upper end of Taneycomo during most of the year. However, beginning around mid-July each year, the cold water coming into Taneycomo from Table Rock routinely has diminished DO levels due to annual biological processes known as stratification that occur over the summer in Table Rock. This summer, the dissolved oxygen levels in in the deeper water of Table Rock were further reduced by a combination of the decomposition of nutrients that were flushed into Table Rock heavy rains in the area and high levels of water generation through Table Rock dam that depleted the oxygenated water in the lake much faster.

This low-DO water is transferred to Taneycomo through flood-control Table Rock Dam and, unlike the water flowing into Shepherd of the Hills Hatchery, cannot be injected with liquid oxygen if power generation is not occurring. Therefore, DO levels drop to near zero during times of non-generation and trout in Taneycomo begin to be impacted negatively. The lack of DO, combined with high amounts of nutrients in the water, is also the culprit for the foul odor some Taneycomo anglers have reported smelling. It should be noted some autumn trout mortality occurs at Taneycomo each year as a result of this process, but the high amounts of rain and water generation at Table Rock through the summer has exacerbated the situation this year.

As temperatures become colder; the upper oxygenated layer of water in Table Rock will cool, become denser, and sink. Once surface water temperature reaches the same temperature as on the bottom, Table Rock Lake will turn over, resulting in a more even distribution of dissolved oxygen throughout all layers of the lake. The release of this water into Taneycomo will help solve that reservoir's problems.

In Missouri, from both a participant and economic perspective, trout fishing is significant. According to a 2011 survey (the most recent data available), trout fishing has more than 277,000 participants in Missouri who spend 1.4 million days fishing each year. This trout fishing activity in the state generates retail sales of $104 million and has an annual economic impact of $187 million. Trout fishing also supports more than 2,300 jobs.

Overall, fishing (all types) in Missouri generates about $677 million in retail sales and has an overall impact of approximately $1.2 billion annually.

More information about trout and about other fishing opportunities in the state can be found at mdc.mo.gov/fishing.