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How Do Low Water Flows Affect Fish?

By Bruce Ingram

Photos by Bruce Ingram

Recently, I received an email from an angler who was concerned about the low fall flows on the Rappahannock River. So on the Rap as well as other Virginia rivers, how much do skinny water conditions affect smallmouth bass and other gamefish as well as the prey they feed on? For this answer and others, I contacted Virginia Department of Wildlife Resources (DWR) Regional Fisheries Biologist John Odenkirk.

“Autumn low flows are not overly impactful to existing fish populations,” he said. “In fact, this situation could possibly help smallmouth bass and other gamefish get a growth bump as they go into winter, as their prey species are more vulnerable. The one downside is that lower, clearer water may make gamefish and their prey a little more vulnerable to avian predators.”

On the other hand, would low water be beneficial to gamefish during the spring spawning period?

“Overly low or high water in the spring has a lot more negative effect on gamefish in rivers than reservoirs,” Odenkirk responded. “In our rivers, normal spring water levels are crucial to spawning success, especially in May when smallmouth and many other gamefish are often on their beds. In short, if we have overly high or low water then, we’re not going to get a good year class.”

Odenkirk says that normal water level conditions basically involves the Goldilocks Principle. If the Rappahannock or other state rivers are too swift and high in May and June, the fry are often swept away and eventually die or fall prey to predators. If the water is too low, fry are often so concentrated that they again are easily found and eaten. Lakes rarely experience such extreme flows unless an impoundment has to be drawn down for some reason.

“Climate change is part of why we’ve had such crazy water flows over the past decade or so, which has resulted in a lot of poor year classes,” Odenkirk continued. “Many long-time fishermen and observers of the Rappahannock have said that they’ve never seen the Rappahannock and many of its tributaries so low.”

Another question the reader had was: does low water affect the “fall feeding frenzy” that fish are reputed to go on as winter nears?

“I don’t know of any paper or study that has investigated that question,” Odenkirk replied. “But I can state that fish are creatures that do not plan ahead. They are creatures of instinct and opportunistic predators. They feed heavily when the barometric pressure, water temperatures, light conditions and other factors are favorable to them finding prey… no matter the season or water level.”

One gamefish that can become extremely negatively impacted when low water exists, specifically if that condition is accompanied by overly warm water, is Virginia’s native brook trout, said Odenkirk. Anglers can help brookies and other gamefish have a better chance of survival after they are released.

“When fish are stressed for whatever reason, anglers should minimize a fish’s time out of the water,” the biologist said. “That means handling a fish as little as possible and releasing a fish as soon as possible. Plus, foregoing the taking of pictures or maybe just taking one quick picture, for example.”

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  • November 6, 2023