Lake Sallie is a 1,273-acre polymictic lake which reaches a maximum depth of 50 feet, with 45% of its surface area is considered littoral. Lake Sallie is classified as a borderline eutrophic lake vulnerable to nutrient impairment. The Pelican River passes through the lake, entering on the north end from Muskrat Lake, outlet into on the south end to Lake Melissa.
Historically, Lake Sallie has had poor water quality, partly due in part to the City of Detroit Lakes use the upstream St. Clair Lake as a discharge point for wastewater. Prior to the construction of the original wastewater treatment facility 1929, untreated wastewater was discharged in the Lake St. Clair, which resulted in phosphorus level in Lake Sallie to be approximately 54ppb, nearly 3 times that of nearby and similar lakes. In 1979, the facility was upgraded. Sallie responded with a decline in phosphorus levels ranging from 46 to 48ppb. The current facility, upgraded in 2002, further reduced load to Lake Sallie resulting in the current mean summer levels between 35 and 37ppb.
While it has greatly improved since the 1970’s it continues to exhibit moderate to severe algal blooms are common, often continuous in July and August. These appear to be brought on in part by internal nutrient recycling, whereby nutrient rich water from the bottom layers are brought to the oxygen rich upper layers during lake mixing periods, often triggered by storm event and high winds.
Much of the nutrient load comes from upstream sources, specifically from nutrient rich water from partially drained Lake St. Clair via Becker County Ditch 14. A ALUM treatment in Lake St. Clair conducted in 1998 reduced internal loading to the lake, and in effect, reduced nutrient loading to the downstream Muskrat and Sallie Lakes. Stormwater Best Management Practices in the City of Detroit Lake has also aided in Lake Sallie improvements be reducing stormwater runoff loads to Little Detroit Lake, which outlets to Sallie.
A lock and dam system was between during the depression era by a Civilian Conservation Corp (CCC) crew between Lake Sallie and Muskrat Lake. This structure was removed in 2001 and replaced be a constructed rapid outfall at the historic water outlet elevation and no longer allows for any water level manipulation. The Pelican River flows out to Lake Melissa through a culvert under Becker CSAH 22 approximately 200 feet downstream of Lake Sallie. The velocity of flow between the outlet of Sallie and the culvert suggests that the headwater of the culvert may be slightly lower than the true water level in the Lake. There is also a slight hydraulic restriction that appears to control lake level.
Contributing land area draining to Lake Sallie in composed primarily of forest, 34% (570 acres), and grassland, 27% (455 acres). Developed land accounts for 19% (316 acres), cultivated crops at 14% (241), and 117 acres (7%) or wetlands.
The mid-season mixing of Lake Sallie and its effect on water clarity, was apparent before and after the July 11th storm event. Prior to the storm event (July 10th) the lake was stratified with a 9.5 foot water clarity. On July 11th, a storm producing wind gusts up to 53 mph came through the region. During the event, lake mixing occurred, causing a significant amount of algal growth and reduction of water clarity to 5 feet, nearly a 50% decline. Following the event, the lake rebounded and ended the year with average water quality. Overall, the 2017 water clarity was better than average with nearly a 9.5 feet clarity and 24ppb total phosphorus (7.75 foot and 35 ppb averages).