Boulder

Boulder is a 3,260-acre reservoir located 12 miles north of Duluth, MN, and can be publicly accessed at the terminus of Boulder Dam Road. Maximum depth is 18 feet and lies in the Cloquet River watershed and is located just upstream of Island Lake Reservoir, near headwater reaches of the Otter River watershed. Boulder is operated as a water storage reservoir by Minnesota Power and is subject to water-level manipulation. The reservoir was constructed in 1919 and overfilled several smaller natural lakes, including Boulder, Little Boulder, and Otter lakes. The 2024 Lake Management Plan (LMP) identifies Walleye as the primary management species. Walleye have not been stocked in Boulder since 1991 due to adequate natural reproduction. The LMP goals for Walleye are to maintain high gill net catch rates (greater than 9.5 fish per lift) with a balanced size structure, and the availability of some large Walleye exceeding 20 inches. Anglers can help achieve this goal through selective harvest and proper catch-and-release techniques. To help estimate spawning success and evaluate future year-class strength, a fall young-of-the-year (YOY) Walleye electrofishing assessment was conducted on Boulder in October 2025. This annual survey provides information on the abundance and average length of Walleye from the juvenile year classes. A total of 445 YOY Walleye averaging 5.5 inches were captured, resulting in a historical high catch rate of 358.7 fish per hour of electrofishing. Previous YOY catch rates have ranged from 13.6 to 325.3 per hour, with a long-term average of 136.8. The abundance of YOY Walleye captured suggests that the 2025 year-class may be very strong. A total of 12 age-1 Walleye averaging 8.7 inches were captured, yielding a catch rate of 9.7 per hour of electrofishing. Historical catch rates for age-1 Walleye have ranged from 5.2 to 72.5 per hour, with a long-term average of 23.6 per hour. The below-average catch rate of age-1 Walleye suggests the 2024 year class may be weaker than average. With three consecutive strong years of YOY catch rates, Walleye angling on Boulder is expected to remain strong in 2026 and beyond, offering anglers opportunities to catch good numbers of quality fish.

A fall young-of-the-year (YOY) Walleye assessment was conducted on Boulder Lake Reservoir on 10/2/2024. Boulder young-of-the-year (YOY) and age-1 Walleye have been indexed annually with night electrofishing since 2002. These data are important as an early indicator of Walleye year-class strength for Boulder. Boulder has not been stocked with Walleye since 1991 because the population has been able to adequately sustain itself through natural reproduction. A total of 298 YOY Walleye with an average length of 5.5 inches were captured during the 2024 investigation for a catch rate of 238.9 per hour of electrofishing. Catch rates from previous investigations ranged from 13.0 to 325.3 per hour of electrofishing. Average length from previous investigations ranged from 3.7 to 6.2 inches. Average length at the end of the first growing season has been strongly correlated to survival to age-1 in other area lakes. The above average size and above average abundance of YOY Walleye suggests that a strong year-class from 2024 is possible for Boulder Reservoir. A total of 22 age-1 Walleye were also sampled for a catch rate of 17.6 per hour of electrofishing. Catch rates from previous investigations ranged from 2.2 to 62.9 per hour of electrofishing. Average length of age-1 Walleye was 9.3 inches. Previous average lengths for age-1 Walleye have ranged from 7.6 to 10.7 inches. The average size and abundance of age-1 Walleye captured suggests that an average year-class from 2023 is likely for Boulder Reservoir.

A fall young-of-the-year (YOY) Walleye assessment was conducted on Boulder Lake Reservoir on 9/28/2023. Boulder young-of-the-year (YOY) and age-1 Walleye have been indexed annually with night electrofishing since 2002. These data are important as an early indicator of Walleye year-class strength for Boulder. Boulder has not been stocked with Walleye since 1991 because the population has been able to adequately sustain itself through natural reproduction. A total of 298 YOY Walleye with an average length of 4.3 inches were captured during the 2023 investigation for a catch rate of 325.3 per hour of electrofishing. Catch rates from previous investigations ranged from 13.0 to 261.5 per hour of electrofishing. Average length from previous investigations ranged from 3.7 to 6.2 inches. Average length at the end of the first growing season has been strongly correlated to survival to age-1 in other area lakes. The below average size but above average abundance of YOY Walleye suggests that a strong year-class from 2023 is possible. A total of 9 age-1 Walleye were also sampled for a catch rate of 9.8 per hour of electrofishing. Catch rates from previous investigations ranged from 2.2 to 62.9 per hour of electrofishing. Average length of age-1 Walleye was 8.0 inches. Previous average lengths for age-1 Walleye have ranged from 7.6 to 10.7 inches. The below average size and abundance of age-1 Walleye captured suggests that a weak year-class from 2022 is likely for Boulder Reservoir.

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

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

Boulder has a maximum depth of 18 feet and a mean depth of 8.1 feet, per Minnesota DNR data.

The most recent Minnesota DNR survey data for the main sport fish in Boulder is from 2023.

No invasive species are on record for Boulder in Minnesota DNR data. Always clean, drain, and dry your equipment to help keep it that way.