Sentinel Lake Assessment Report Portage Lake (29-0250) Hubbard County, Minnesota

The Minnesota Pollution Control Agency (MPCA) is working in partnership with the Minnesota Department of Natural Resources (MDNR) on the Sustaining Lakes in a Changing Environment (SLICE) Sentinel Lakes Program. The focus of this interdisciplinary effort is to improve understanding of how major drivers of change such as development, agriculture, climate change, and invasive species can affect lake habitats and fish populations, and to develop a long-term strategy to collect the necessary information to detect undesirable changes in Minnesota Lakes (Valley 2009). To increase our ability to predict the consequences of land cover and climate change on lake habitats, SLICE utilizes intensive lake monitoring strategies on a wide range of representative Minnesota lakes. This includes analyzing relevant land cover and land use, identifying climate stressors, and monitoring the effects on the lake's habitat and biological communities. The Sentinel Lakes Program has selected 24 lakes for long-term intensive lake monitoring (Figure 1). Portage Lake was selected to represent a shallow eutrophic lake in the Northern Lakes and Forest (NLF) ecoregion. Portage Lake is a 170 hectare (422 acre lake), located approximately 5 miles north of Park Rapids, Minnesota in west central Hubbard County, within the Crow Wing River watershed. The lake has a maximum depth of 5.2 meters (17 feet) and a mean depth of 2.3 meters (7.6 feet). The lake is 97% littoral with one public access on the southern shore of the lake. The total contributing watershed for Portage Lake is 1,210 hectares (2,995 acres). Portage Lake is located within the NLF ecoregion, but is very close to the transition to the North Central Hardwood Forests (NCHF) ecoregion. Portage Lake is a relatively shallow lake that mixes during high winds and weakly stratifies during calm periods. Based on recent water quality data (2007-2008), Portage Lake is considered to be eutrophic with total phosphorus (TP), chlorophyll-a (chl-a), and Secchi values of: 60 micrograms per liter (μg/L), 21 μg/L, and 0.9 meters (3 feet) respectively. TP is particularly high and exceeds the typical ranges (based on reference lakes) for both the NLF and NCHF ecoregions. Nuisance algal blooms were common and transparency was typically low during much of the summer. Trophic status data collected by the lake association since 1997 suggest slight increases in nutrient levels and algal growth over time and in particular for the recent period from 2004-2008. As a result, Secchi transparency has declined slightly as well. Based on these data, Portage Lake was included on the 2006 303(d) (Impaired waters) list that Minnesota submitted to the United States Environmental Protection Agency (EPA). A Total Maximum Daily Load (TMDL) study is targeted to begin for Portage Lake in 2014. Once a lake is placed on the Impaired Waters List it is required to be intensively researched through a TMDL study to determine the source and extent of the pollution problem followed by the development of a restoration plan.