Ross Island Lagoon (RIL) has a long history of manipulation, beginning in the 1940s when an embankment was constructed that shut off downstream flow into the lagoon. A private gravel operator subsequently removed millions of cubic yards of material from the lagoon, leaving a very deep (120’) hole in the river. These activities have contributed to a Harmful Cyanobacterial Bloom (HCB) at RIL, which is occurring with increasing frequency and intensity, and has led to the ODEQ listing of the lagoon as impaired for cyanobacteria. The lagoon produces toxins and genomic data suggests it contributes to blooms that occur throughout the lower river. Health advisories are increasingly issued and 2021 brought stunningly high concentrations of toxins (150 mg/L, relative to the 8 mg/L recreational contact limit) to the river. In 2023, the entire lower Willamette River was under an advisory for the HCB. Simultaneously, efforts are underway to restore shallow water habitat for outmigrating juvenile salmon. However, routes into those lagoon habitats are extremely limited for the subyearlings that need it, and the bloom impairs water quality (e.g. pH> 9.5) during the early summer when fish could be using those habitats. A solution is needed to both address the human health risk and the need for expanding shallow water habitats for juvenile salmon in the lower Willamette.
These HCBs are produced under conditions of elevated water temperature, excess nutrients, and stagnant water. As climate chaos continues, water temperatures will continue to rise and reducing nutrients is difficult and slow. At RIL, reconnecting the lagoon to the river and eliminating the stagnant water solves multiple problems, addressing the HCB, improving water quality, and enhancing rearing habitat access for Lower Columbia steelhead and Chinook, while also minimizing operation and maintenance of in-river infrastructure.
The RIL HCB is unique due to its occurrence in river, and solutions to the HAB are complicated by environmental, regulatory, and logistical constraints. OSU faculty and students have been supporting invested parties in identifying potential solutions for addressing the HCB. This work involved years of collaboration, careful collection and analysis of field data, and numerical modeling of ecological processes in the lagoon. Multiple alternatives were compared. Regulators, scientists, engineers, and other invested parties were consulted. The end result is a clear but complicated solution: Reconnecting the lagoon to the river offers the best solution at resetting and restoring ecological processes in this urban setting.
Want to learn more? Please see our StoryMap for a summary. Resources on Ross Island history, regulations, and science are here.