Sediment & Nutrients

Bear Lake is often dubbed the ‘Caribbean of the Rockies’ for its blue color. However, the lake faces a silent threat: sediment from the Bear River is slowly but steadily altering the lake. This sediment introduces suspended solids and excessive nutrients that lead to the overproduction of algae and bacteria, resulting in cloudy water.

*The statistics above occur during the spring and summer runoff when the Bear River is allowed to flow directly into Bear Lake.

This isn’t just a matter of aesthetics; it’s about preserving an ecosystem that supports a wide variety of fish species and other wildlife. According to studies from the Idaho Department of Environmental Quality (DEQ), nutrient pollution can cause significant water quality problems including harmful algal blooms which not only degrade recreational enjoyment but also pose risks to human health.

Bear Lake Watch funded a research project studying the sediment dynamics of the Bear River-Mud Lake-Bear Lake system in partnership with Utah State University’s Department of Watershed Sciences and the US Fish and Wildlife Service. The study was concluded in 2018.

Bear Lake’s unique water quality is reliant on the Bear River, which both deposits and removes water from Bear Lake, and Mud Lake, which serves as a “buffer between Bear River and Bear Lake” (Belmont et al., 2018).

Researchers examined past data and collected new information concerning the Bear River-Mud Lake-Bear Lake system. Their goals were to further understand the system, to identify how the system has and may evolve, what parts of the system have degraded or are at risk of degradation and to pinpoint future research areas.

The functioning of the Bear River-Mud Lake-Bear Lake system is essential to keeping unwanted sediment out of Bear Lake.

The Dingle Marsh is a “natural wetland system” that “has played a large role in connecting the River and Lake” (Belmont et al., 2018). The Dingle Marsh filters unwanted sediments and nutrients from the Bear River before the water reaches Bear Lake.

However, the effectiveness of the Dingle Marsh has dwindled drastically since 1909, when Telluride Power implemented the ‘Bear Lake Project,’ a plan to construct canals between Bear River and Bear Lake through the Dingle Marsh. The project was completed in 1917, and made it possible for water to be pumped out of Bear Lake and for water to be diverted from Bear River “into Bear Lake for storage and release to accommodate downstream agricultural irrigation and hydroelectric power demands” (Belmont et al., 2018).

A major obstacle to these uses arose due to the inconsistent nature of river flow, as the majority of the water was snow runoff. PacifiCorp devised a plan to pump water from the Lake that worked around this inconsistency, further impacting the Dingle Marsh. This plan had three phases: first, water was moved from the inlet to the causeway and stored in Mud Lake and Bear Lake during the “storage phase.” Second, water flow through the causeway was decreased and flow through the outlet was increased for the purpose of downstream irrigation, primarily during the summer in the “lake fill and downstream release” phase. Lastly, water was moved from the inlet to the outlet and pumped out of Bear Lake in the “lake pumping phase” (Belmont et al., 2018).

The Bear Lake Settlement Agreement of 1995 and the Amended Bear Lake Settlement Agreement of 2004 reduced the amount of water that PacifiCorp could pump from Bear Lake. Additionally, the PacifiCorp Agreement of 2000 gives PacifiCorp specific water levels that must be maintained, in order to avoid retreating levels, especially during seasons of drought. However, the act of pumping water from the lake still has an impact on wildlife, recreation and water quality throughout the entire Bear River-Mud Lake-Bear Lake system.

This can be seen in the Dingle Marsh, which used to be a “freshwater system” (Reeves, 1954). It still filters some sediments and nutrients before they reach the lake. However, the Dingle Marsh is not performing its function as well as it used to since the building of the canals. As such, each time the “lake fill and downstream release” phase takes place, sediment enters the lake (Belmont et al., 2018).

Mud Lake is an “open-water area in the southeast corner of Dingle Marsh” and performs an important part in filtering sediment and nutrients from Bear River, before water enters Bear Lake. The efficacy of this filtering system can vary from year to year depending on river flow. In 1989, Bjornn et al. reported that the Dingle Marsh filtered 70% of suspended solids. In 2008, however, Allen and Mesner found that only around 50% of suspended sediment was being trapped by the Dingle Marsh. Additionally, sedimentation rates in Mud Lake have either increased or stayed stagnant. While these findings show that Mud Lake will continue to serve as a “net sediment trap” between Bear River and Bear Lake, because the sedimentation rates have increased, the amount of sediment loading to Mud Lake and Bear Lake has also most likely increased (Belmont et al., 2018).

The sources of sediment have also changed due to the building of canals in 1917. After the canals were built, levels of nearly all of the Rare Earth Elements and Transition Metals loading into Mud Lake increased significantly. Additionally, in around 2008, there was another sudden increase in silver and mercury, specifically. While researchers were were unsure if these elements were being delivered by sediment through the Bear River-Mud Lake-Bear Lake system or through “atmospheric deposition,” the high levels of these elements have an impact on the “health of the Mud Lake and Bear Lake ecosystems” (Belmont et al., 2018).

The water quality of Mud Lake also changed drastically after 1917. In an examination of the species of algae found in Mud Lake, it was found that in around 1917 the algae species were habitable to mesotrophic lakes, meaning that the water quality and nutrient levels are moderate. However, there is evidence that for years before the canals were built, Mud Lake was dominated by a species of algae that preferred low nutrient waters, showing that water quality is declining.

Additionally, researchers examined the Bear Lake shoreline as another potential source of sediment. They found that the shoreline has “moved inward, indicating deposition in various locations around the lake at both high and low lake levels” (Belmont et al., 2018). Additionally, it was noted that there was an increase in vegetation on the lake shore, specifically in the northwest corner of the lake, close to the St. Charles Creek. Around 10% of an area that was a sandy beach in 2003 was completely covered by vegetation in 2016. Researchers faced time restrictions and were unable to identify the specific type of vegetation. However, some types of vegetation play a significant role in “nutrient and carbon dynamics,” while other types of vegetation are invasive and thus harmful to lake ecosystems (Belmont et al., 2018). Bear Lake’s beaches are often covered by water, thus preventing the growth of vegetation; additionally, humans may remove vegetation. Researchers are now investigating the “beach-vegetation dynamics” of Bear Lake (Belmont et al., 2018), and their impact on the sediment load.

We must take action now to reduce this sedimentation process before it permanently alters our precious lake. Bear Lake Watch is calling on local authorities to implement effective measures aimed at reducing sediment and nutrient inflow into Bear Lake.