Cottonwood Lake is a class 28 lake located near Deer River, MN. Cottonwood Lake has one unnamed inlet that originates from a wetland and no outlets. There is a public access on the south side of the lake. The initial lake management plan established in 2009 indicates bluegill and black crappie as the primary species of management with northern pike as a secondary species. The 2013 assessment included additional sampling of near shore fish species in order to calculate an Index of Biotic Integrity (IBI) score and these data are documented in a separate report.
Black crappie catches were at a record high for Cottonwood Lake. The gill-net catch was 15.3 while the trap-net catch was 7.3 fish/net; both well above normal for this type of lake. The trap net sampled fish ranged from 4.3 to 9.8 inches and averaged 6.5 inches. The gill-net sampled fish had a similar size distribution. Seven age-classes from 2 to 8 years old were identified from scales. The 2010 year class dominated the sample, representing nearly half of the fish. Growth was poor compared to other class 28 lakes with fish averaging 8.1 inches after five years of growth.
Trap-net catch rates for bluegill were 29.8 fish/net; also a record high for Cottonwood Lake. Bluegill lengths ranged from 3.2 to 8.7 inches and averaged 6.1 inches. Ten age-classes were identified from scales ranging from age 2 to age 11. Growth rates were similar to other class 28 lakes but required more than seven years to attain 7.0 inches. Growth and potentially size structure was likely better when catches were lower.
The 2013 assessment was the first year that electrofishing was used to sample largemouth bass in Cottonwood Lake. The catch was 25.5 fish/hr of sampling. Largemouth bass ranged from 6.1 to 17.7 inches with an average length of 11.1 inches. Eight year-classes were identified from scales ranging from age 2 to age 10. Growth was similar to the statewide averages for all ages.
Northern pike gill-net catch rates have ranged from 9.5 to 16.8 fish/net since 1977. Although the 2013 catch was the lowest on record (9.5 fish/net), it remained above the lake class 3rd quartile. The gill net sampled fish had poor size structure, ranging from 17.3 to 29.1 inches with a mean length of 22.1 inches. Seven year-classes were identified from cliethra and scales ranging from age 2 to 9. Northern pike averaged 20.8 inches by age 4 which was similar to the statewide average of 20.5.
Other species observed during the population assessment included bowfin, golden shiner, hybrid sunfish, pumpkinseed sunfish, rock bass, yellow bullhead, and yellow perch. Additional species observed while sampling for IBI included banded killifish, blackchin shiner, central mudminnow, Iowa darter, Johnny darter, least darter, and longear sunfish.
In order to maintain or improve fish and wildlife populations, water quality and habitat must be protected. People often associate water quality problems with large-scale agricultural, forestry, urban development or industrial practices in the watershed. In reality, the impact of land use decisions on one lake lot may be relatively small, yet the cumulative impact of those decisions on many lake lots can result in a significant decline in water quality and habitat. For example, removing shoreline and aquatic vegetation, fertilizing lawns, mowing to the water's edge, installing beach sand blankets, failing septic systems and uncontrolled run-off, all contribute excess nutrients and sediment which degrade water quality and habitat. Understanding these cumulative impacts and taking steps to avoid or minimize them will help to insure our quality fisheries can be enjoyed by future generations.