6-01-2023 3:38pm

Trout Unlimited Asking Fisherman to Refrain Fishing Dexter’s Mill Creek During Hot Temps

Mill Creek in Dexter. Photo by Doug Marrin.

Ann Arbor Trout Unlimited (AATU) asks anglers to refrain from fishing Mill Creek in Dexter during high temperatures.

Brown trout, like other trout species, are cold-water fish that experience physiological stress when water temperatures reach around 68°F (20°C). This stress increases rapidly as the temperature rises further. For many fishermen, 70°F (21°C) has become a round figure representing the "don't fish" limit1.

The upper limits of the temperature range within which trout will feed, grow, and remain unstressed by thermal conditions can be misleading. These upper limits characterize thermal conditions under which otherwise unstressed trout will die should those thermal conditions persist for a certain period, typically 24-48 hours. Warmer water contains less oxygen than colder water. As temperature rises and dissolved oxygen decreases, fish begin to experience stress. These stresses begin well before the water temperature reaches lethal limits.

One study conducted in Idaho showed that the mortality was 69% higher for trout landed in 73-degree water than for those taken from water 66 degrees or less. Even in catch-and-release situations, abnormally high-water temperatures can be lethal to fish under respiratory and other forms of stress due to being hooked and played by an angler.

Furthermore, low water levels often exacerbate the effect of high-water temperatures on brown trout. A combination of low water levels and hot sunshine leads to high water temperatures and low oxygen levels. Once the water temperature reaches 20-21°C (68-70°F), brown trout struggle and even best practice catch and release can result in unintended mortality. This is because the stress of being caught and then released can overwhelm the fish, especially when water temperatures are high.

The AATU emphasizes that by refraining from fishing in Mill Creek during high-temperature periods, anglers will play a crucial role in preserving the health and resilience of our cherished brown trout population.