Reservoirs are large man-made water storage facilities, but also vibrant aquatic ecosystems that contain fish. These human-made lakes, or enlarged natural lakes, serve various purposes, from providing drinking water and irrigation to generating hydroelectric power and controlling floods. Beyond their utility, reservoirs also function as habitats for diverse fish populations, supporting natural ecological processes and recreational activities.
How Fish Enter Reservoirs
Fish populate reservoirs through natural processes and human intervention. Natural pathways involve existing aquatic connections. Fish can swim into newly formed reservoirs from upstream or downstream rivers and streams that were dammed. Flooding events can also play a role, temporarily connecting separate bodies of water and allowing fish, their eggs, or even young fish to be carried into new areas.
Less common, fish eggs can be transported by animals. Waterfowl, such as ducks and herons, may inadvertently carry sticky fish eggs on their feet or feathers. Once deposited, these eggs can hatch and establish a new fish population. While natural colonization can occur, it often takes time for a diverse and stable fish community to develop.
Stocking is a primary method for establishing and maintaining fish populations in reservoirs. State agencies and other organizations intentionally release fish into these waters for various reasons, including recreational fishing opportunities, conservation efforts, and sometimes to manage water quality. This practice ensures a robust fish community, especially where natural colonization might be slow or insufficient.
Types of Fish Found in Reservoirs
Reservoirs host a wide array of freshwater fish species, with types depending on climate, water temperature, and regional management programs. Many common game fish species thrive, including warmwater species like largemouth bass, smallmouth bass, sunfish (such as bluegill), crappie, and catfish. These fish prefer warmer temperatures and are found in the shallower, upper layers of reservoirs.
Coolwater species tolerate a broader temperature range but prefer cooler conditions, inhabiting many reservoirs. Examples include yellow perch, walleye, and northern pike. In colder climates or deeper reservoirs, coldwater species like trout (e.g., rainbow, brown) can be found. These fish require cooler, more oxygenated water, often found in deeper, stratified sections.
What Helps Fish Thrive in Reservoirs
Environmental and management factors are important for supporting healthy fish populations in reservoirs. Water quality is important, encompassing temperature, dissolved oxygen, and clarity. Reservoirs often experience thermal stratification, with warmer water near the surface and colder water deeper down, which influences where different fish species reside. Adequate dissolved oxygen is necessary for fish survival, as low levels can stress or kill fish.
The physical structure of a reservoir also creates important habitat. Submerged features like old river channels, standing timber, rock piles, and artificial structures provide shelter, feeding grounds, and spawning areas. These structures offer protection from predators and strong currents, and they support the aquatic insects and smaller fish that form the base of the food web. The availability of varied habitats allows different species to coexist and thrive.
Fisheries management practices are important for sustaining reservoir fish populations. This includes regulations like catch limits and size restrictions to prevent overfishing and allow fish to reach reproductive maturity. Habitat improvement projects, like adding artificial structures or planting aquatic vegetation, can enhance the reservoir’s capacity to support fish. Ongoing stocking programs also ensure desired species are present in sufficient numbers, especially when natural reproduction might be limited.