Ocean Shores consultants report high phosphorus, propose targeted units and tools to curb toxic algae

Katie Sweeney Rodriguez, an environmental scientist with Herrera Environmental Consultants, told a public meeting in Ocean Shores that a year of monitoring shows the city’s lakes and canals remain nutrient-rich and prone to cyanobacteria (toxic algal) blooms despite improvements since the 1990s.

“This project is to develop a plan for improving the water quality and the fresh waterways of Ocean Shores,” Sweeney Rodriguez said, summarizing the purpose of Herrera’s fresh waterways management work for the city.

Herrera’s preliminary monitoring (summer–fall 2024 plus early 2025 sampling) revisited sites from a 1994 KCM study and added additional lake, canal and watershed stations. The consultant measured temperature, dissolved oxygen, pH, total phosphorus, chlorophyll a, Secchi depth (water clarity), cyanobacteria species and, at watershed sites, E. coli, total suspended solids, chloride and flow. Herrera reported: chlorophyll a values in 2024 generally fell in the eutrophic range (2024 site range: about 1–26 µg/L versus 1994 range of about 10–32 µg/L); total phosphorus remained high at many sites (1990s site averages ranged roughly 50–2,000 µg/L; 2024 averages roughly 59–1,000 µg/L at monitored stations); and the system overall remains eutrophic to hyper-eutrophic.

Herrera detected cyanobacteria species across multiple waterbodies and tested four bloom samples for cyanotoxins. Microcystin was detected in samples from the Lake Menard area and the south Grand Canal/marine boat-launch area; anatoxin‑a was not detected in the 2024 samples. Of the four cyanotoxin tests collected by city and county public-health staff, Herrera reported one exceedance of state guidance that would trigger a public-health advisory.

The consultant said the monitoring and historical work point to multiple phosphorus sources but emphasized shallow groundwater as a dominant pathway. “Shallow groundwater aquifers were providing most of the phosphorus in the system,” Sweeney Rodriguez said, noting buried peat and high-organic deposits under the peninsula that leach phosphorus into groundwater and connect directly with surface waters.

Herrera presented eight proposed management units so treatments and responses can be tailored: Lake Menard; Bell Canals; North Grand Canal; South Grand Canal; Fish Hook Canal and the south end of Duck Lake; middle Duck Lake; north Duck Lake; and Bass Canal. The consultant recommended a two-track approach: reduce phosphorus inputs where feasible and, where blooms occur, mitigate risks and symptoms.

Proposed watershed and in‑lake strategies included: continued sewer connections and stormwater best-management practices (fertilizer reduction, pet‑waste pickup, shoreline planting); aquatic-plant harvesting; phosphorus inactivation treatments (aluminum sulfate, lanthanum-modified clays and other formulations, including zero‑valent iron, which Herrera said merits further evaluation); targeted algaecide use for short-term public-health protection; aeration/oxygenation systems; mixing and circulation devices (including solar-powered units); and, where appropriate, limited dredging. Herrera cautioned that dredging is costly, difficult to permit, can temporarily mobilize phosphorus, and could increase groundwater–surface water interaction if done improperly.

Costs and longevity varied by method in Herrera’s presentation: algaecides and modular mixers can be implemented at relatively lower initial cost (single- to tens-of-thousands of dollars per unit or event) but are typically short-term; phosphorus inactivation treatments can range from tens to hundreds of thousands and can last years; oxygenation installations can cost hundreds of thousands to millions and require ongoing power and maintenance. Herrera characterized emerging options such as sonication, micro/nanobubbles, ozone, and certain biological or straw-based approaches as experimental with mixed or limited case‑study evidence.

Local residents asked questions about toxins, public communication, harvesting, carp impacts, the golf course and whether dock-level pumps or homeowner circulation devices would help. Sweeney Rodriguez said harvesting does remove phosphorus bound in plant biomass and can be part of a program, but it does not stop continuous external loading from groundwater and some creeks. On public messaging, she urged stronger surveillance and communication and offered a simple public-health tagline used in other places: “When in doubt, stay out.”

Becky (city staff) and participants asked about prioritizing canals, potential pilot trials and homeowner actions such as reduced fertilizer use; the consultant said those watershed measures are cost‑effective and would be included in the plan. Herrera also noted operational constraints for treating groundwater phosphorus: “There’s no point source we can treat from — it’s coming in from everywhere,” Sweeney Rodriguez said, which raises costs and complexity for direct groundwater treatment.

Herrera said the freshwater‑ways management plan will: summarize monitoring and past studies, set measurable water‑quality objectives (examples Herrera floated included reducing blooms to fewer than two per year, limiting bloom duration to under three consecutive weeks and reducing the number of bloom years in any 10‑year span), identify recommended management actions with rough timelines and cost ranges, and include an adaptive‑management framework. Herrera intends to return with a draft plan in late spring (May–June) and deliver a final plan in June; city staff will compile public questions submitted to a city email address and coordinate follow-up.

The meeting included public discussion but no formal vote or adoption of specific measures. Herrera and city staff asked residents to submit additional input by email for incorporation into the plan.