Little Rock Lake is a 1,270 acre shallow lake located in the North Central Hardwood Forest (NCHF) Ecoregion in a transitional area between forested and agricultural areas. The lake has an average depth of eight feet and a maximum depth of 16 feet.
The lake basin began as shallow wetland, and evolved into a vegetated marsh following the construction of a dam on the Mississippi River downstream of the Little Rock Creek outlet in 1907. Water levels were raised in 1934, further evolving the lake basin from a vegetated marsh into a turbid impoundment. As a result of the dam installation, waters levels increased over 15 feet in some places with Little Rock Lake water levels increasing over 7 feet.
It has been over 100 years since the initial impoundment, and water levels have not been allowed to fluctuate more than 6 inches above or below 1014 MSL. Without the natural drought cycle with rising and falling water levels, valuable plant growth expansion is not possible.
The lack of shoreline stability plant growth would provide along with the land use changes from scrub/shrub, wetland, and forested, to now largely agricultural has contributed to the significant increase in nutrients, sediment loading, and algal blooms currently effecting Little Rock Lake.
Water clarity and algae blooms driven by exceptionally high phosphorus levels have been a concern for the lake since at least 1990. However, an extreme blue-green algae bloom in 2007 (Figures 9 and 10) produced toxin microcystin to the point that it became an acute public health risk around the lake and downstream to the residents of St. Cloud.
Phosphorus levels as high as five times greater than the standard acceptable amount, and chlorophyll-a levels 11 times greater than the standard have been recorded resulting in persistent water clarity depth readings of only a few inches. The insistent algal issues in Little Rock Lake is the worse known regionally, and is in the top 4% of the most polluted lakes in the state.
Little Rock Lake TMDL
As a result of the extreme blue-green algae bloom in 2007, Little Rock Lake was listed as impaired in 2008 and subsequent plans including the nutrient TMDL and TMDL Implementation Plan were developed and completed in 2012 and 2013, respectively. The TMDL indicates that the highest concentration of phosphorus and other nutrients are seen during spring runoff with animal waste being a significant source, other sources include; internal loading, septic loads, greywater, and streambank/shoreline erosion. A daily average nutrient load reduction of 13.2 kg/day (29.10 lb/day) would be required to meet Minnesota's water quality standard for shallow lakes in the North Central Hardwood Forest Ecoregion. The TMDL sets an interim phosphorus reduction goal at 5,375 pounds (35%) and a final phosphorus reduction of 7,927 pounds (53%) is necessary to meet state water quality standards. A combination of external and internal implementation strategies are recommended for the restoration of Little Rock Lake, beginning with emphasis on external sources. In 2013 an Implementation Plan was developed to address stressors and their sources for both the Little Rock Lake TMDL and Little Rock Creek TMDL.
Little Rock Lake & Creek Watershed TMDL Implementation Plan
The TMDL indicates that a combination of external and internal implementation strategies will be necessary with long term strategies involving “farm management to minimize excess phosphorus (fertilizer + animal feed – crop export – animal export)… coupled with traditional best management practices (BMPs) to reduce surface runoff and phosphorus transport from feedlots and cropland”.
Benton and Morrison SWCDs have a history of successfully installing Best Management Practices in the Little Rock Watersheds. Both districts have taken a leadership role in the coordination and implementation of BMPs, water quality and quantity projects, and programs. Since the development of the TMDL, a significant effort has been put forth to address external phosphorus sources, and over 70 BMPs have been installed in the watershed
Water Quality Monitoring
Benton SWCD is currently in year two of a three year monitoring plan for Little Rock Creek and other tributaries to Little Rock Lake including; Bunker Hill Creek and Sucker Creek to evaluate our progress towards meeting watershed load reduction goals. This monitoring plan consists of bi-weekly chlorophylla, total phosphorus (TP), total suspended solids (TSS), BOD5, and nitrate nitrogen, and total Kjeldahl nitrogen (TNK) samples as well as stream flow, pH, stream temperature, and dissolved oxygen measurements. A consultant was hired to evaluate the monitoring data each year to develop water quality progress reports. We will use these reports to evaluate the effects of watershed BMPs and other variables, and apply the adaptive management concepts in the implementation plan by adjusting implementation activities in future years.
Little Rock Lake Association
Little Rock Lake Association has been monitoring the Lake since 2012. Water chemistry samples for total phosphorus, chlorophyll-a are taken monthly along with secchi depth water clarity measurements. The short period of record does not allow for statistically significant trend analysis at this time. While no statistically significant long term trend can be evaluated yet, 2017 data shows improvements over 2016 data for total phosphorus, chlorophyll-a, and secchi depth. When this data is visually compared with data from the TMDL study, it suggests that watershed BMPs are resulting in improvements in lake water quality. Consistent with the implementation plan, this signals the need to begin installing second priority implementation activities, including aquatic plant management.
For more information on Little Rock Lake monitoring:
For more information on the Little Rock Lake Association:
Minnesota Pollution Control Agency
The Minnesota Pollution Control Agency (MPCA) has initiated the Watershed Restoration and Protection Strategy (WRAPS) for the Mississippi River – Sartell watershed. This intensive watershed strategy will involve both monitoring and modeling. Numerous sites on Little Rock Creek and Bunker Hill Creek, and tributaries to Little Rock Lake, will be sampled during the WRAPS process. The WRAPS is anticipated to be completed in 2020. Sampling in the Little Rock Lake watershed will consist of biological (fish and invertebrates) and water chemistry, along with habitat assessments and flow monitoring.
For more information on MPCA monitoring and the WRAPS process:
Little Rock Lake Drawdown Feasibility Study