Wetlands can fulfill many fish needs because of their functions, such as providing habitat, producing food, and cycling nutrients. The most important wetland functions for fish survival are food production, spawning and nursery habitat, refuge, and the reduction of harmful pollutants in water.
As a general rule, the deeper the water in the wetland and the more its hydrology is connected with lakes and rivers, the more likely the wetland is to support fish.
Source: Wetlands and Fish: Catch the Link, National Oceanic and Atmospheric Administration (NOAA)
Fish Habitat Quality
Generally, the value of a wetland for fish habitat is related to its connection with deep water habitats. A wetland has a high value for fish if it provides spawning/nursery habitat, or refuge for native fish species in adjacent lakes, rivers or streams. Some isolated deep marshes may intermittently support populations of sunfish and northern pike as a result of colonization during flood events. Permanently flooded isolated wetlands that support native populations of minnows provide moderate value.
Spawning habitat for warm water species can be an important function of a wetland, and northern pike are among the most valuable warm water species spawning in wetlands.
Northern pike wetland spawning habitat will have several characteristics including:
A semi-permanent or permanent connection to a lake or stream that has a population of northern pike;
The wetland is vegetated primarily with reeds, grasses, or sedges; or secondarily with cattails, rushes, arrowhead, water lilies, submerged plants, and shrubs or lowland hardwoods with grass and low emergents;
The wetland is flooded during the early spring at least once every 3 years for at least 20 days and remains connected to the lake or stream during that time;
Lacustrine areas should have 4 to 8 acres of actual spawning area for each 100 littoral acres of lake; and
Shallow or deep marsh wetland spawning areas are typically located on the upstream side of the lake or stream.
Wetlands with exclusive, high carp populations provide low value for fish habitat because carp cause extreme degradation of the wetland.
Isolated wetlands that are not permanently flooded do not generally support fish populations.
Source: Minnesota Routine Assessment Method (MnRAM), Version 3.4, Minnesota Board of Water and Soil Resources