Rock

A targeted survey of nearshore fish species in Rock Lake, was conducted on August 11th, 2025, by Area Fisheries staff. Sampling sites were evenly spaced around the lake, and each was sampled by backpack electrofishing and seining with a 50-foot or 15-foot seine, where possible. Backpack electrofishing was completed at 10 sampling stations. Similarly, a 50-foot seine was used to sample 1 station, and a 15-foot seine was used at 5 stations. Four stations were not seined due to deep water and dense lilies. Nearshore sampling captured 12 species of fish including no species that are intolerant of disturbance and 1 species that is tolerant of disturbance (i.e., Green Sunfish). The nearshore data were combined with trap net and gill net data from an August 2016 survey to describe the fish community and provide a fish-based IBI (FIBI) score. The FIBI uses fish community data to measure a lake's health, and the types of fish species present can help identify any stressors that may be negatively affecting the lake environment. In Minnesota lakes, certain fish species cannot survive without clean water and a healthy habitat (e.g., Blackchin Shiner, Iowa Darter, and Rock Bass), while other species are tolerant of degraded conditions (e.g., Green Sunfish and Common Carp). The FIBI score, composed of several fish community diversity and composition metrics, indicates the overall health of a lake by comparing it to what is expected for a healthy lake. For additional information on the FIBI, search for "lake index of biological integrity" on the mndnr.gov website. Results from this survey provide evidence that the fish community in Rock Lake is adversely impacted by stressors, as indicated by an FIBI score below the general use impairment threshold for aquatic life use determined for similar lakes. These results are similar to previous findings which indicated that Rock Lake is impaired for biological health. The survey results will be considered when the biological health of the lake is assessed during the North Fork Crow River watershed assessment process, which will be completed in coordination with MN Pollution Control Agency. You can help protect the fish community in Rock Lake by reducing runoff, maintaining natural shorelines, and preventing the spread of invasive species.

Rock Lake was stocked with Walleye fingerlings prior to 1997 and then stocked annually with fry from 1997-2000. After this was deemed unsuccessful, Rock Lake has been stocked with Walleye fingerlings or yearlings biennially since 2001. It was scheduled to be stocked in 2024, but surplus fry were available in the spring of 2024 and 50,000 fry were stocked into Rock Lake on a trial basis. During the day on September 10th, 2024, 90 minutes of electrofishing produced no walleye fingerlings. Thirty-eight adults were observed, ranging from 12.9 to 26.4 inches. Fry stocking was deemed unsuccessful and Rock Lake was subsequently stocked with 235 pounds of fingerlings (1,041 fish) by the Minnesota DNR. Rock Lake will continue to be stocked with Walleye fingerlings every other year.

Rock Lake was stocked with Walleye fingerlings prior to 1997 and then stocked annually with fry from 1997-2000. After this was deemed unsuccessful, Rock Lake has been stocked with Walleye fingerlings or yearlings biennially since 2001. It was scheduled to be stocked in 2024, but surplus fry were available in the spring of 2024 and 50,000 fry were stocked into Rock Lake on a trial basis. During the day on September 10th, 2024, 90 minutes of electrofishing produced no walleye fingerlings. Thirty-eight adults were observed, ranging from 12.9 to 26.4 inches. Fry stocking was deemed unsuccessful and Rock Lake was subsequently stocked with 235 pounds of fingerlings (1,041 fish) by the Minnesota DNR. Rock Lake will continue to be stocked with Walleye fingerlings every other year.

Based on Minnesota DNR survey data, anglers target Largemouth Bass, Walleye, Northern Pike, Black Crappie, and Green Sunfish in Rock. See the full species list above for catch rates, size structure, and quality scores.

Minnesota DNR records list public access for Rock. Check the DNR LakeFinder page for the launch type and directions before you go.

Rock has a maximum depth of 37 feet and a mean depth of 13.6 feet, per Minnesota DNR data.

The most recent Minnesota DNR survey data for the main sport fish in Rock is from 2016. Surveys this old should be treated with some caution — fish populations change over time.

Yes — Rock has confirmed Eurasian watermilfoil. Clean, drain, and dry your equipment to avoid spreading invasives to other waters.