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After the 2018 watershed assessment, the Iowa DNR began to work with a private engineering firm, FYRA Engineering Inc., to identify additional restoration practices that can be implemented within the watershed as well as in-lake improvements that can lessen sedimentation from the lake’s agriculture-intensive watershed and ultimately improve the lake’s water quality. Two new embankments will be constructed in critical areas of the Three-Mile Lake Wildlife Management Area (WMA). Three existing ponds on the Three-Mile Lake WMA will be dredged to increase capacity for sediment retention. Three-Mile Lake has a large (25 acres) sediment/nutrient retention basin at the upper end of the reservoir. However, over time this basin has become full of sediment that is beginning to spill over into the lake. FYRA is investigating options to improve this structure either through targeted dredging, raising the elevation of the silt dam, or constructing a secondary silt basin below the existing structure. The option selected to improve this important structure will depend on United States Army Corps of Engineers permitting as well as available funding. Two additional in-lake silt basins will also be constructed in reservoir tributaries that receive considerable sediment/nutrient delivery.

In addition to the sediment catchment basins, the Three-Mile Lake stakeholders plan to prevent shoreline erosion into the lake due to wind and wave action. Shoreline erosion can lead to increased turbidity and negatively impact the lake’s water quality. The water level will be lowered by a maximum of 12 feet beginning in fall 2022 for shoreline improvements. Many areas of the shoreline are eroding into the lake leading to water clarity issues. Over 1,300 feet of shoreline in critical need of repair will be deepened and armored with Class E rip rap. An additional up to 13,000 feet of shoreline will be armored with Class E rip rap to prevent future shoreline erosion into the lake. Fishing jetties are popular locations for shoreline anglers to access the lake. Two of the 10 existing fishing jetties will be extended and three of the fishing jetties will be benched to create improved shoreline fishing opportunities for anglers.

While the lake is lowered in 2022-2024 for in-lake restoration activities (shoreline armoring, construction of in-lake silt basins, etc), new rock fish habitat structures including 30 gravel spawning areas, 20 rockpiles, 10 rock fields, 10 rock reefs, and five extra wide rock reefs will be constructed to improve rock fish habitat in Three-Mile Lake. The spawning areas will consist of small limestone chips placed in 18-42 inches of water for panfish species such as Bluegill Lepomis macrochirus and Crappie Pomoxis spp.to use to deposit their eggs and guard their nests. These nearshore spawning areas are not only beneficial to panfish species for reproduction, but can also be fish attractors for anglers. Rockpiles, rock fields, and rock reefs are constructed using Class E rip rap placed at varying water depths to create unique underwater structures for sportfish. The crevices created by the congregation of rock attract aquatic invertebrates which then attracts sportfish for foraging. These structures not only provide panfish with cover from predator sportfish, but can also act as fish attractors for anglers. These structures are marked with a GPS and the coordinates are uploaded to the Iowa DNR’s Interactive Fishing Atlas (https://programs.iowadnr.gov/maps/fishingatlas/default.html ) so that anglers can locate these structures in real time. Over 1,300 feet of shoreline in critical need of repair will be deepened and armored with Class E rip rap. An additional up to 13,000 feet of shoreline will be armored with Class E rip rap to prevent future shoreline erosion into the lake. The shoreline improvements will not only prevent future water quality issues, but will also provide some additional underwater rock habitat for sportfish. Fishing jetties are popular locations for shoreline anglers to access the lake. Two of the 10 existing fishing jetties will be extended and three of the fishing jetties will be benched to create improved shoreline fishing opportunities for anglers.