In 2024 initial pilot temperature and oxygen profiles were taken on a subset of heritage trout lakes over three trips taken along the general mapped route below. We didn’t collect a full season of data on any of the lakes, but some of our (preliminary) observations include:
- Many of the lakes remained strongly thermally stratified late into October, a result that was unexpected but perhaps not surprising with the warm weather we experienced. Lake trout spawn in the fall, so we are curious about how the warm, shallow water impacts spawning;
- Gillis lake, which is an important heritage trout lake for various reasons, had excellent oxy-thermal habitat all through the late summer and fall;
- Powell Lake, which is listed as a heritage trout lake but has not been surveyed in 30 years, appeared to have little, if any, suitable trout habitat in early fall; and
- Elm Lake, which has never been surveyed, appears to have the depth and oxy-thermal habitat to support lake trout. Headwaters Project created the first known detailed maps of Elm Lake (see below), and we hope to learn more about it in 2025.
In 2025 the Headwaters Project plans to undertake work to further understand these lakes and begin to build a long-term understanding of the lakes with monthly temperature profiling of a subset of lakes, depth mapping of up to four heritage trout lakes, and selective water sampling.
These trips will occur on May 22nd to 25th, June 26th to 29th, July 24thto 27th, August 16th to 24th,September 25th to 28th, and October 23rd to 26th. Staffing will include Headwaters Research Team members, primarily college undergraduates. Each trip will typically include 3 to 5 Research Team members, who will help prepare for the field work, conduct the field trips, and assist in data processing. Typically different students will comprise each field research team.
The focus of the 2025 field season will be the following:
- Oxygen/Temperature Profiling. Obtain high quality data on the temperature and oxygen depth profiles of key heritage trout lakes during the open water season. Such data will form a baseline understanding how heritage lakes are stratifying and warming over the season, plus how much suitable habitat exists during peak periods of thermal stress.
- Lake Depth Mapping – Bathymetric mapping of up to four heritage trout lakes that do not currently have available lake depth maps. These lakes are Wisini, Strup, Blue Snow and Gillis Lakes.
- Environmental DNA Pilot – Use environmental DNA (eDNA) methodologies to begin proof of concept for tracking the presence of the following relevant species in heritage trout lake: lake trout, smallmouth bass, walleye, spiny water flea, and zebra mussels.
More detail on each element is described below:
Lake Temperature and Oxygen Profiling
2025 will include lake temperature and oxygen profiles taking from May until October, with lakes divided into two tiers as described below.
Tier 1 Lakes:
Resources do not allow for monitoring of all of Minnesota’s heritage trout lakes repeatedly during the summer, so a subset of lakes have been selected for their varied depths, shapes, and known fish populations. This subset of lakes includes one of the deepest lakes in Minnesota (Gabimichigami), one of Minnesota’s most important lakes from which trout stock has been collected (Gillis) and a series of small, varied trout lakes.
The Tier 1 circuit can be completed in approximately four days. Tier 1 lakes will be sampled six times at monthly intervals from May through October. The lakes in Tier 1 comprise (in order of measurement): Brant Lake (Entry Point 52), Fay Lake, French Lake, Peter Lake, Gabimichigami Lake, Howard Lake, Little Saganaga Lake, Elm Lake, West Fern Lake, Powell Lake, Fern Lake, Gillis Lake, Bat Lake, Owl Lake, and Tuscarora Lake.
Tier 1 Lakes trips on the following dates:
- May 21-24 – Tier 1
- June 26-29 – Tier 1
- Jul 24-27 – Tier 1
- Sept 25-28 – Tier 1
- Oct 23-26 – Tier 1
Tier 2 Lakes:
Lakes are to be sampled in late August at the time of expected peak thermal stress. Tier 2 lakes include all Tier 1 lakes, plus an additional two dozen lakes, mostly north and west of the Tier 1 lakes.
The Tier 2 Lakes trip will be on the following dates:
- August 16-24 – Tier 2
Equipment used will be a YSI ProSolo DO/T probe. Measurements will be made in the deepest point in each lake at 1 meter increments, recorded the YSI ProSolo with a backup manual record on paper.
Lake Depth Mapping
Up to four lakes will be sounded in 2025 using a Lowrance HDS 9 sounder with GPS capabilities.
The MNDNR bathymetric mapping specialist has provided the MNDNR manual on lake depth sounding, and the Headwaters mapping protocols will follow the MNDNR manual. In 2024 Headwaters Project, working with Voyageur Maps, created the first high quality map of Elm Lake, which has not been fully sounded before and which may contain lake trout (no one knows, but we hope to find out).
Headwaters Project Elm Lake mapping results:
The lakes to be mapped in 2025 are:
- Strup Lake
- Wisini Lake
- Gillis Lake
- Blue Snow Lake
Strup and Wisini lakes will be mapped as part of the Headwaters Young Scientist Initiative (YSI), with Gillis and Blue Snow mapped by Headwaters Field Research Team undergraduate students on one or more trips in addition to the Tier 1 and Tier 2 trips (Gillis is a Tier 1 lake. Blue Snow is a very inaccessible lake that is listed as a Heritage Trout Lake by Minnesota DNR records but has not been sounded and does not have permanent portage access).
Environmental DNA Assessments (eDNA)
Environmental DNA (eDNA) is genetic material shed into the environment by organisms, such as through skin cells, scales, or mucus. In aquatic systems like lakes and rivers, this DNA can be collected from water samples and analyzed to detect which species are or were recently present—without needing to catch or observe them directly.
Extensive research has been conducted on the use of eDNA for fisheries assessments, including to detect the presence of fish and invasive species.
Benefits of eDNA for conservation and management include the following:
- Non-invasive: No harm to fish or habitats.
- Cost-effective: Reduces the need for expensive or intensive field surveys.
- Highly Sensitive: Detects even low-density populations.
- Rapid Detection: Enables quicker management decisions when new or harmful species are detected.
eDNA is particularly suitable to the Headwaters Project because it allows for a relatively low-cost way to assess what organisms are in the heritage trout lakes, and can be applied to neighboring lakes and water bodies.
Most heritage trout lakes have only been infrequently assessed by the Minnesota DNR, since such assessments have historically involved setting of nets to capture fish. Some heritage trout lakes have only been assessed once in 50 years! Also, such assessments are expensive in terms of staff time, and excessive assessments could have a negative impact on the fish populations since these are small lakes with very slow growing fish.
eDNA can be used for determining the presence of lake trout, but perhaps just as important can look for non-native organisms, of which (maybe surprisingly) the two most problematic are likely smallmouth bass and walleye, neither of which are native to these lake trout lakes. Walleye and smallmouth bass have been expanding in scope throughout northern Minnesota, and the result has been a loss of native lake trout population. eDNA won’t solve the spread of non-native fish, but understanding where non-native fish have spread allows resource managers to make decisions on how to potentially slow or stop their expansion.
Traditionally eDNA has been processed using expensive equipment beyond the scope of small projects. However, in recent years there has been growth in lower cost options, some that cross between education and research environments.
In 2025 the Headwaters Project will be using equipment from MiniPCR (www.minipcr.com) to undertake pilot work to see if we can accurately identify the presence of trout, walleye, smallmouth bass, and possibly other species. Pilot work in 2024 identified PCR primers for identifying lake trout. This year we’ll work to develop protocols and experience with other targets (walleye and bass) and water sampling techniques.