TMDL Launched for Big Sandy and Minnewawa Lakes...

Scenery shot of the Big Sandy Lake Watershed.A body of water is considered “impaired” or polluted if it fails to meet one or more of the federal Clean Water Act’s water quality standards. Minnesota’s Impaired Waters list includes Big Sandy, Minnewawa, Eagle, and Island Lakes within the Big Sandy Lake watershed.

The state’s current approach to solving the problem of water pollution is developing Total Maximum Daily Loads (TMDLs) - a pollution reduction plan. The TMDL process identifies all sources of the identified pollutant and determines how much each source must reduce its contribution in order to meet the water quality standard. The sum of all contributions must be less than the maximum daily load.

Project Summary: In 2006, Big Sandy and Minnewawa Lakes in Aitkin County were placed on Minnesota’s 303(d) List of Impaired Waters, for aquatic recreation due to excessive nutrients. The data indicated that these lakes had total phosphorus concentrations in excess of the MPCA’s state water quality standard of 30 micrograms per liter, for the growing season mean. 

In the spring of 2008, a TMDL study was launched for Big Sandy and Minnewawa Lakes. The first step is assessment of the waterbody. Throughout the summer, extensive water quality samples were taken on each lake. This information, along with stream data, will be used to determine the level of impairment and pollutant reductions that are needed to restore the quality of the lakes. 

This project includes the following components:

  • water quality and sediment monitoring,
  • watershed and in-lake quality response modeling,
  • calibrating the modeling to the most recent monitoring data,
  • reviewing the water quality goals for the lakes,
  • evaluating watershed control measures and in-lake management techniques for phosphorus load reductions,
  • determining the margin of safety and specific waste load and load allocations for each source of phosphorus,
  • recommendations for implementation and compliance monitoring plans. 
  • The TMDL Report, and stakeholder/technical advisory meetings will also be completed as part of this project.

Background Information: The Big Sandy and Minnewawa Lakes TMDL study is located in north central Minnesota and extends across Aitkin, Carlton, and St. Louis counties. Landuse within the watershed is typical of what is found in north-central Minnesota. Forests make up approximately 63% of the watershed, wetlands and water 21%, agriculture (pasture and cultivated land) 14%, and urban 2%. This study lies within the Northern Lakes and Forests Ecoregion of Minnesota.Temperature & Dissolved Oxygen Profiles were taken at each lake site.

Big Sandy Reservoir was formed by closure of the dam on the Sandy River in 1886. The watershed extends eastward from the Mississippi River about 26 miles and is about 18 miles wide in the north-south direction. Four main river systems constituting over 150 river miles contribute water to Big Sandy Reservoir: the West Savanna from the north, the Prairie and Tamarack Rivers from the east, and the Sandy River from the south. The Big Sandy Watershed has abundant water resources, including 49 lakes. 

A Kemmerer sampler is used to take lake water samples at specified depths in the lake.Lake Sampling: Three lakes were sampled during the summer of 2008. These include Big Sandy, Minnewawa, and Horseshoe Lakes. Sampling on Big Sandy Lake included three sites – one in the main basin, one in Webster’s Bay and one in Bellhorn Bay. Two sites on Lake Minnewawa were sampled – one on the main basin of the lake and one in the north arm. Just one site on Horseshoe Lake was monitored. Samples were analyzed for Total Phosphorus, Total Dissolved Phosphorus, and Chlorophyll a. Secchi depth, lake level, and water column profile data (dissolved oxygen, temperature, and conductivity) were also measured throughout the summer.

The Prairie River sampling location on County Road 14.Stream Sampling: Eight stream sites were also monitored during 2008. Data gathered at these sites will be used to determine sources of nutrients entering the lake. The sites include:

  • Sandy River, at Pier 65 on HWY 65
  • Sandy River , on HWY 65 just north of McGregor
  • Minnewawa Creek, on HWY 65 near the junction with CR 6
  • Prairie River, on the North Road in Balsam Township
  • Prairie River, on the South Road in Balsam Township (includes the Tamarack River watershed)
  • Prairie River, on CR 14
  • Savanna River, on CR 14 near Savanna Portage State park
  • Inlet to Horseshoe Lake, on CR 40
  • Samples were analyzed for Total Phosphorus, Total Dissolved Phosphorus, Total Suspended Solids, Suspended Volatile Solids, and Turbidity. Transparency Tube, temperature, dissolved oxygen, conductivity, and pH information was also gathered for each site. 

What’s next?: A plan for implementing this TMDL has been developed and approved by the MPCA. This plan outlines steps that will be taken in an effort to bring Big Sandy and MInnewawa Lakes back to good health. Project partners have worked to develop this plan, and will cooperate on implementing the identified objectives. To view this plan, click this link: 
Big Sandy Minnewawa Implementation Plan

To learn more about impaired water and TMDLs, visit the MPCA’s web site at Available on the website are examples of Final TMDLs and Implementation Plans, as well as informative publications. For local information, please feel free to contact the Aitkin County SWCD at (218) 927-7284.