As is typical of a large flood control reservoir as described in the RFHP “Reservoir Fish Habitat Management” manual, sedimentation carried into the basin from a vast drainage is a key issue to deal with for fisheries management. "Unlike natural lakes, reservoirs tend to have large watersheds and large tributaries because they were engineered to capture as much water as possible to serve flood control…. Depositional filling effectively results in surface area and volume reductions, habitat fragmentation, loss of depth, and associated changes in water quality. Unnatural water-level fluctuations interact with wave action to degrade shorelines that were once uplands and are unable to withstand continuous flooding, which promotes erosion and ultimately homogenization of once diverse littoral habitats. Lack of woody debris deposition in the littoral zone, limited access to adjacent backwaters, and lack of seed banks and stable water levels to promote native aquatic vegetation characterize barren littoral habitats in many reservoirs" (2017 Dr. Miranda, Reservoir Fish Habitat Management, 1.1 Introduction).

This is the perfect assessment of conditions at Lake Red Rock and describes how the current habitat conditions have been formulated. Once the dam began operations, reservoir inflows and water level fluctuations exceeded expectations. Natural lake bottom structures began to degrade or even disappear and sediments started to accumulate, which created a muck/silt substrate, which over several years has become a predominately featureless stratum and virtually no aquatic macrophyte presence.

The Red Rock Reservoir drainage area is a vast watershed covering over 12,300 square miles in central, north central and northwest Iowa, with a large percentage of that surface area in some form of agriculture production in private ownership. The dam is situated on the Des Moines River, but several tributaries coalesce into one inflow upstream from the confluence with Lake Red Rock. The reservoir is prone to high inflows of water with large amounts of suspended sediment, which adversely affects lake depth. The upper reaches of the reservoir, west of State Highway 14, are mostly less than 4 feet in depth (Figure 2.) with many acres of exposed mud flats where inflows are beginning to slow (Figure 3.), but due to these flash inflows, sediment is dispersed throughout the lake. Littoral zones are also impacted from suspension of shoreline particulate from wave action and fluctuating water conditions (Figure 4.).

Fully understanding the management strategies of Lake Red Rock is not possible without knowing about the reservoirs involvement in the Sustainable Rivers Program (SRP). SRP is a nationwide partnership, initially organized by the Corps of Engineers and The Nature Conservancy, to find ways to operate dams and other Corps owned and operated infrastructure in more environmentally friendly ways. In 2016 Red Rock hosted a two-day environmental flow and pool management workshop with biologists, stakeholders and other scientific experts to learn what primary ecological concerns they had with the Des Moines River. Eight recommendations were realized from the workshop: Reduce nitrate levels, mussel mortality, sturgeon mortality (downstream), gas bubble trauma, downstream bank erosion; and improve conditions for migrating water birds, conditions for reptiles and amphibians, and conditions for downstream river recreation. These recommendations were influential in a revised lake regulation manual.

To accommodate the above-mentioned recommendations and other environmental conditions, a conservation band was incorporated into the regulation manual to enable the Corps to adjust pool levels to benefit a biological purpose either in the lake or for downstream conditions. The Corps developed an Adaptive Management and Monitoring Plan (AMMP), along with assistance from partners and stakeholders. In-lake water level management strategies and environmental flows downstream of the dam are specific elements of the AMMP that seek to support fish and mussel life histories. Many successful environmental flows and research studies have sprung from that plan and it is regarded as a model for dams and reservoirs across the country. Currently, Lake Red Rock is one of four designated SRP Science project sites. SRP is funding the Iowa State University Cooperative Research Unit to conduct a 2-year research program associated with the fisheries, mussels, and their habitat in the Des Moines River, with the goal of evaluating how fisheries and mussel resources respond to the operations of Red Rock Dam. This data will be utilized in the adaptive management of dam operations and continued refinement of the Des Moines River Adaptive Management and Monitoring Plan.

Ongoing SRP efforts also work to find solutions that address nitrification and other water quality concerns within the Des Moines River. Early research on the denitrification ability of Lake Red Rock from 1974-2019 has concluded that the reservoir has reduced nitrates 12% from incoming flow to its release through the dam. Through a contract with the University of Iowa, Hydroscience & Engineering, the Corp hopes to further understand this process and how pool management may influence denitrification. In a complimentary effort, the USACE has partnered with the Natural Resources Conservation Service (NRCS) to find ways to reduce nutrient inputs into the lake. Thirty-three watersheds encompassing Red Rock and Saylorville Lake, another USACE flood control reservoir situated on the Des Moines River, just upstream of the city of Des Moines, have been assessed to determine locations where soil conservation structures could exist, and opportunities for modifications to land use practices or soil conservation structures to reduce the nutrient and sediment input to the reservoirs. Two websites have been developed that utilize arc gis mapping to evaluate watershed features and assist landowners to implement the Best Management Practices (BMP) for soil and water conservation measures and improve the Lake Red Rock watershed via a Watershed Resilience Tool.

See: https://usace-mvr.maps.arcgis.com/apps/MapJournal/index.html?appid=f18bdd82e2404d50b4c30c5b1d25da00
and: https://usace-mvr.maps.arcgis.com/apps/mapviewer/index.html?webmap=a5cdc7b440d747099ea110eb4622c494
Other statewide programs, targeted initiatives and watershed associations are also attempting to address water quality issues and reduce sedimentation. Saylorville Lake tends to trap sediments from the upper portions of the Des Moines River, preventing those sediments from reaching Lake Red Rock. The North and South Raccoon Rivers merge northwest of the city of Des Moines and empty into the Des Moines River on the south side of the city. Several Watershed Management Authorities (WMA) are active in the upper reaches of the Red Rock Lake drainage (Figure 5.), providing resources to improve water quality (Figure 6.).

Two tributaries, Whitebreast Creek and Competine Creek flow into Lake Red Rock from the southwest, creating two separate arms adjacent to the main lake (Figure 7.). The conditions exhibited in the main lake are mirrored in these two separate arms, but not to the extent as seen in the larger portion of the reservoir. The combined watershed for these two tributaries is just over 275,000 acres versus several million acres for the Des Moines River (Figure 8. Blue highlighted Red Rock Watershed is 1.55 million acres, but does not include the Raccoon River watershed). The Iowa Department of Agriculture and Land Stewardship (IDALS) provides cost share money to landowners in the Lake Red Rock watershed for Best Management Practices (BMP) that curb run-off and soil loss, which directly impact the water quality and sediment load flowing into the lake (Figure 9. K. Ament IDNR). As illustrated on the IDALS spreadsheet (Figure 9. K. Ament IDNR), the number of implemented practices and total dollars spent in the Whitebreast and Competine Creek watersheds is practically equal to the practices and monies spent in the larger Red Rock watershed. This demonstrated level of support for water quality measures is part of the reason for primarily targeting the Whitebreast Creek and Competine Creek arms for fish habitat enhancement.