Mary

A targeted survey of nearshore fish species in Mary Lake was conducted beginning on July 1, 2024, by Index of Biological Integrity (IBI) Program 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 all 10 sampling stations. A 50-foot seine was used to sample 7 stations and a 15-foot seine was used at 3 stations. Nearshore sampling captured 10 species of fish, including 2 species that are intolerant of disturbance (Blacknose Shiner and Rock Bass). A concurrent summer trap net survey was also conducted by IBI Program staff. Nine trap nets were set along the shoreline in locations that encompassed multiple habitat types. Trap net sampling captured 14 species of fish, including 1 species that is intolerant of disturbance (Rock Bass). Bluegill and Black Crappie comprised a majority of the catch by number, whereas Bowfin comprised a majority by biomass. Northern Pike, Walleye, White sucker, and Yellow Bullhead were few in number, but each species comprised a significant proportion of the trap net biomass. The nearshore and trap net data were combined with gill net data from a survey conducted in July of 2023 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 Mary Lake is adversely impacted by stressors, as indicated by an FIBI score near the impairment threshold for aquatic life use determined for similar lakes. The survey results will be considered when the biological health of the lake is assessed during the Pine River Watershed assessment process, which will be completed in coordination with MN Pollution Control Agency. Mary Lake supports several popular game fish species, including Black Crappie, Largemouth Bass, Northern Pike, and Walleye. These species can make for good angling opportunities. However, the sunfish population in Mary Lake is relatively low and with poor size structure. Additionally, shiners and darters were collected in low numbers in the nearshore survey. These findings may be cause for concern. You can help protect the fishery in Mary Lake by reducing runoff, maintaining natural shorelines, and preventing the spread of invasive species.

Public access to Mary can be obtained by coming up the Little Pine River from Emily Lake. One fish species you are likely to catch in Mary Lake is black crappie. Numbers were high in 2023 at 23.3/gill net, however, the size left a lot to be desired. Only 9% were larger than 8". Size and numbers were low for the other common panfish species, bluegill. Average length was 5.7", with 26% larger than 7" and 5.6 were caught per net. The lake association has stocked walleye fingerlings into Mary on a regular basis since 2006. Walleyes could also migrate from connected Emily Lake which is stocked with walleye fry. Walleyes were caught in average numbers (1.5/gill net) for this type of lake. All the fish were over 13" and had an average length of 21.3". Northern pike were also of decent size, with an average length of 24.2" and 44% of the fish above the 22-26" protected slot. Numbers were below average however at 3.0/gill net.

Nearshore: A targeted survey of nearshore fish species in Mary Lake was conducted on August 17-24, 2022, by DNR Index of Biological Integrity (IBI) Program 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 eight sampling stations, but two stations were sampled from the boat due to site conditions. Similarly, a 50-foot seine was used to sample six stations, a 15-foot seine was used at two stations, and site conditions prevented the use of seines at two stations. Nearshore sampling captured 14 species of fish including one species that is intolerant of disturbance (i.e., Rock Bass) and none that are tolerant of disturbance. The nearshore data will be combined with trap net and gill net data from a survey planned in 2023 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, Blacknose shiner, and Rock Bass), while other species are tolerant of degraded conditions (e.g., Black Bullhead, Common Carp, Fathead Minnow). 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. Data from this survey will contribute biological information about the health of the fish community to the Pine River Watershed assessment process in coordination with MN Pollution Control Agency. Score the Shore: Minnesota DNR Fisheries IBI program staff conducted an assessment of lakeshore habitat on Mary Lake on Sep 1, 2022 following the Score the Shore survey protocols. The assessment consisted of 38 survey sites evenly spaced 200 meters around the lake. Assessments were made in three habitat zones: Shoreline Zone (the shore-water interface to the top of the natural bank), Shoreland Zone (land-ward from shoreline to development structure or 100 feet), and Aquatic Zone (lake-ward 50 feet of shoreline). he average lakewide habitat score was 74.6 (±3.6) out of 100 possible, which is moderate and near the statewide average score of 73. A moderate score indicates a a high percentage of unaltered habitat but may lack an aspect of critical habitat. Approximately 68% of the sites were developed with a mean score of 65.2 (±4.1), while undeveloped sites had a mean score of 95.0 (±1.2). FLEM: Minnesota DNR Fisheries IBI program staff delineated the floating leaf and emergent aquatic vegetation of Mary lake 09/07/2022, following the protocols listed in the MN DNR Lake Plant Mapping Manual. There were a total of 35.8 acres of floating and emergent plants mapped. This consisted of 19.7 acres of emergent dominated plant communities and 16.1 acres of floating leaf plant communities. The following taxa were noted during the survey: Robbins' spikerush (Eleocharis robbinsii), bulrush (round-stem group) (Schoenoplectus spp.), bur-reed Floatingleaf Group (Sparganium spp.), burreed Emergent Group (Sparganium spp.), cattail (Typha spp.), sedge (Carex spp.), three-square bulrush (species) (Schoenoplectus pungens), watershield (Brasenia schreberi), white waterlily (Nymphaea odorata), wild rice (Zizania palustris), yellow waterlily (Nuphar variegata). For more information see map and summary table below.

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

We don't have a confirmed public access point on record for Mary. Check the DNR LakeFinder page for current access details before you go.

Mary has a maximum depth of 34 feet, per Minnesota DNR data.

The most recent Minnesota DNR survey data for the main sport fish in Mary is from 2024.

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