McMahon

McMahon is a 187-acre (158 littoral acres) lake with a maximum depth of 14 feet. McMahon is located south of the City of Prior Lake in southeast Scott County. McMahon is primarily managed for Bluegill and Largemouth but includes catchable populations of Black Crappie, Northern Pike, and Walleye. Public water access (concreate ramp; up to 9 vehicle/trailer parking spaces) is located on the northwest side of the lake off of county road 87 and is maintained by DNR Parks and Trails. A Standard Survey (9 trap nets/5 gill nets) was conducted on McMahon Lake during the week of 6/23/2025 to monitor water characteristics and fish populations. Water color was brown/green, with moderate water clarity, measured at 7 feet during the time of this survey. Dissolved oxygen fell to two parts per million at 14 feet. Eurasian Watermilfoil has been identified in McMahon Lake and remains present, providing a good reminder of the clean, drain, dispose law which helps to prevent the spread of aquatic invasive species: Clean all aquatic plants, zebra mussels, and other invasive species from boats, trailers, and water-related equipment. Drain water from your boat, ballast tanks, motor, live well and bait container. Remove drain plugs and keep drain plugs out while transporting equipment. Dispose of unwanted bait in the trash. To keep live bait, drain the water and refill the bait container with bottled or tap water. High numbers of Bluegill were sampled with trap nets (42.0/net), well above the expected catch rate of similar lakes. There were 378 Bluegill sampled in trap nets during the 2025 survey, with an average length of 5.3 inches and the largest measured at 9.4 inches. Despite high catch rates, Bluegill growth in McMahon was fast compared to similar lakes, indicated by an average length of 5.9 inches by age 3 and 7.8 inches by age 5. Multiple nine-inch Bluegill were sampled during the 2025 survey, demonstrating the potential for a tremendous fishery. Largemouth Bass are present in McMahon Lake, although targeted boat-electrofishing did not occur during the 2025 survey. Incidental capture with trap and gill nets caught 20 Largemouth Bass, with an average length of 12.9 inches and the largest measured at 17.7 inches. Future surveys will include a targeted spring boat-electrofishing component. High numbers of Black Crappie were sampled with gill nets (52.6/net) and trap nets (14.7/net) above the expected catch rates for both gears. There were 302 Black Crappie sampled during the 2025 survey, with an average length of 6.3 inches and the largest measured at 10.9 inches. Over 90% of Black Crappie measured less than 9 inches, likely providing little interest to anglers at their current sizes. Very high numbers of Northern Pike were sampled with gill nets (28.8/net), well above the expected catch rate of similar lakes. The 2025 netting represents the highest catch rate of Northern Pike in McMahon Lake in the previous 30 years. There were 143 Northern Pike sampled in gill nets, with an average size of 21.1 inches and the largest measured at 35.0 inches. Nearly 90% of Northern Pike measured less than 24 inches. The current regulation (minimum size 24"; limit 2) does not currently leave much opportunity for harvest. Moderate numbers of Walleye were sampled with gill nets (5.4/net), near the expected catch rate of similar lakes. There were 27 Walleye sampled in gill nets, with an average length of 21.0 inches and the largest measured at 26.0 inches. Only one Walleye measured less than 17". Stocked Walleye fingerlings may have trouble surviving until the extremely high number of Northern Pike declines. Walleye growth in McMahon was fast early on, indicated by an average length of 11.1 inches by age 2 and 20.5 inches by age 4, and slowed at older ages with an average length of 21.7 by age 7 and 20.8 inches by age 8. Despite inconstant growth, mortality of older sizes is low with Walleye aged to 13, 16, and 19 years old. Other fish species sampled during the survey include Black Bullhead, Golden Shiner, Green Sunfish, and Yellow Perch.

McMahon (Carl's) Lake is a productive 110-acre, Class 43 lake. It is located 6 miles south of the city of Prior Lake, in Credit River Township. The lake is primarily managed for Bluegill and Largemouth Bass, and secondarily managed for Northern Pike, Walleye, and Yellow Perch. The New Market Sportsman's Club stocks Walleye. A Standard Survey was conducted in 2015 to assess the gamefish populations. Bluegill abundance was high in 2015; the catch rate of 24.3 fish per trap net exceeded the third quartile for this Lake Class. The average size of trap-netted Bluegill was 6.1 inches and 0.19 pounds. Thirty-four percent of the fish exceeded 7 inches, and only 2% of the fish exceeded 8 inches. The largest Bluegill was 8.5 inches and 0.45 pounds. Bluegill attained an average length of 6.6 inches by age 3, and 7.3 inches by age 4. Walleye abundance is relatively high compared to other lakes in the West Metro Fisheries Area. The 2015 catch rate of 4.0/gill net fell between the first quartile and median for Class 43 lakes throughout the state. This is a decline from the 2010 catch rate of 6.0 fish per gill net. Walleye mean length and weight were 19.7 inches and 2.74 pounds, with the largest reaching 26.0 inches. Size structure revealed a population of large individuals, with 92% of fish exceeding 15 inches, 54% at 20 inches or longer, and 8% at 25 inches or longer. Walleye reach an average of 15.7 inches by age 4, and 22.0 inches by age 6. Northern Pike were abundant in 2015. The gill net catch rate (11.7/net) exceeded the 75th percentile for class 43 lakes. This decrease in catch from the previous survey (in 2010), when 15.3 fish per net were caught, is also accompanied by an improved size structure since that survey. In 2015, the average Northern Pike was 22.0 inches and 2.58 pounds, an increase from an average size of 20.6 inches and 1.97 pounds. Fifty-seven percent of the 2015 catch exceeded 21 inches, compared with 39% of fish exceeding 21 inches previously. Eleven percent of Northern Pike exceeded 28 inches in 2015, compared with 6% exceeding 28 inches in 2010. The largest fish measured in 2015 was 33.7 inches and 9.35 pounds. The fish reached an average of 20.7 inches by age 3, and 27.2 inches by age 7. Black Crappie abundance was high in gill nets (17.7, above third quartile) and moderately high in trap nets (5.2, between median and third quartile). For both gear types combined, 36% of Black Crappie were 8 inches or longer and the largest fish sampled was 10.6 inches and 0.68 pounds. Average size was 7.3 inches and 0.24 pounds. In 2015, Yellow Perch were moderately high in abundance (20.0/gill net, between median and third quartile) compared with other Class 43 lakes in the state. Mean length and weight were 7.2 inches and 0.18 pounds. Eighteen percent were 8 inches or longer and the largest fish was 10.2 inches and 0.61 pounds. Other species sampled in low abundance included Black Bullhead, Brown Bullhead, Golden Shiner, and Largemouth Bass.

McMahon (a.k.a. Carl's) Lake is a productive 110-acre lake located in Credit River Township, 6 miles south of Prior Lake. A standard population assessment was conducted during the first week in July, 2010 to determine the species composition and abundance of fish in the lake. Walleye abundance is relatively high compared to other lakes in the West Metro Area. At 6.0/gill net, numbers were near the median (6.8/net) for similar lakes throughout the state. Current walleye abundance was similar to the 6.8/net that were observed in the 2004 assessment. Walleye mean length and weight were 18.3 inches and 2.4 pounds, with the largest reaching 26.5 inches. Size structure was high, with 69% at 15 inches or longer, 36% at 20 inches or longer, and 6% at 25 inches or longer. The majority of walleye sampled were from the 2005 (21%), 2006 (14%), and 2007 (31%) year classes. Walleye averaged 14 inches by age 3 and 20 inches by age 5. The New Market Sportsman's Club annually stocks approximately 1000 fingerlings in McMahon Lake to maintain the walleye fishery. Northern pike are very abundant (15.3/gill net). Typical of high northern pike densities, mean weight (2.1 pounds) was moderately low. Size structure is characterized by 39% of northern pike at 21 inches or longer and 6% at 28 inches or longer. Average length was 20.6 inches and the largest sampled was 32.9 inches. The current population size is the highest on record and is supported by the large 2006 and 2007 year classes that make up 80% of the population. Northern pike averaged 21 inches by age 4 and 28 inches by age 6. Black crappie abundance was high in gill nets (34.8/net) and moderately high in trap nets (11.5/net). Gill net catch has varied over previous assessments (range since 1958, 2.0  76.0) however trap net catch is the highest observed since the 1970 assessment (14.8 /net). For both gear types combined, 54% of black crappie were 8 inches or longer and the longest sampled was 9.1 inches. Average length and weight were 7.1 inches and 0.21 pounds. Relatively consistent recruitment was observed with five year classes contributing to the population (2005 through 2009). The 2005 and 2008 year classes were the most abundant contributing 26% and 38%, respectively. Black crappie averaged 8 inches by age 4. Bluegill abundance (80/trap net) is high compared to similar lakes in the state. Catch of bluegill in trap nets has varied over the years. Since 1988 (5 assessments), the number per net has ranged from 44 to 538. In 2010, mean length and weight in trap nets were 6.2 inches and 0.21 pounds. Sixty-one percent were longer than 6 inches with the largest reaching 7.8 inches. Bluegill ranged in age from 2 to 8. The largest year class was in 2005, which represents 37% of the population. Bluegill grew to 6 inches by age 4. Sixteen largemouth bass were collected during the assessment; however, passive sampling gears, such as trap nets and gill nets, are not effective methods for collecting largemouth bass. The data presented for this species is not indicative of relative abundance. Electrofishing is the typical method for largemouth bass assessments but was not conducted during this survey. Mean size was 12.3 inches and 1.37 pounds with the largest reaching 20.4 inches and 4.87 lbs. Fifty-six percent were 12 inches and longer and 19% were 15 inches and longer. Yellow perch are moderately low in abundance (5.17/ gill net) compared with similar lakes in the state. This has generally been the case over the previous four assessments, with the exception of 1993 when 19.2 per net were observed. Mean length and weight were 6.6 inches and 0.12 pounds. Three percent were 8 inches or longer and the longest was 9.3 inches. Most (90%) yellow perch were age 3 or 4. Yellow perch grew to 8 inches by age 4. Golden shiner, an important prey species in the lake that was perhaps established or supplemented by bait dumping, was found in high abundance (24.2/gill net). In addition to being abundant, golden shiners are reaching large sizes. Mean weight was 0.20 pounds. Golden shiners averaged 7.8 inches, the largest measured 9.7 inches. In an assessment of the shallow, nearshore fish community, backpack electrofishing and seining were conducted. The most abundant species observed was young-of-the-year (YOY) bluegill. Additionally, adult bluegill, black bullhead, green sunfish, largemouth bass (adult and YOY), and YOY pumpkinseed were observed. An Index of Biotic Integrity (IBI) was estimated based on all fish sampled in this assessment. The absence of sensitive species such as some minnows and darters contributed to a low IBI score, indicating water quality and habitat may be impaired. Other species sampled included black bullhead, white sucker and yellow bullhead.

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

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

McMahon has a maximum depth of 14 feet, per Minnesota DNR data.

The most recent Minnesota DNR survey data for the main sport fish in McMahon is from 2025.

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