Consultants say Weiser Lake has extreme summer phosphorus, propose short‑ and long‑term fixes

Whatcom County Health and Community Services staff and outside consultants presented a draft lake management plan for Weiser Lake at a virtual public meeting, saying monitoring shows summer phosphorus concentrations far above recommended levels and offering a mix of short‑term and long‑term options.

The consultants said the lake’s West Basin recorded phosphorus concentrations “over 300 micrograms a liter” and the East Basin over 200 micrograms a liter, compared with a typical target of about 20 micrograms per liter to limit nuisance algal growth (Mark Rosenkrantz, Aquatic Insight). The presentation tied those elevated summer phosphorus levels primarily to internal loading—phosphorus released from lake sediments under low‑oxygen conditions—plus continuing inputs from upstream watershed flows, septic systems and seasonal waterfowl movements.

Why it matters: summer cyanobacteria blooms at Weiser Lake have caused very low water clarity and concentrated mats at popular access points, affecting recreation and shoreline use. The plan’s combined monitoring and modeling approach suggests some interventions could reduce blooms quickly, while others—septic upgrades and agricultural best management—would be longer term.

Key findings and evidence

- Monitoring and lab work: County staff and contractors collected seasonal water‑quality samples, sediment cores and biological samples. Consultants used those data in simple lake models (Vollenweider and Nurnberg approaches) and a nutrient budget to estimate sources and likely drivers of blooms.

- Extreme summer phosphorus and internal loading: “We have a phosphorus concentration over 300 micrograms a liter in our West Basin and over 200 micrograms a liter in the East Basin,” said Mark Rosenkrantz, who led the data review. Consultants reported that a substantial fraction of the sediment phosphorus is bioavailable (about 59% in the West Basin and roughly 70% in the East Basin, based on organic and iron‑bound pools) and that chemistry and overnight low dissolved oxygen can mobilize that phosphorus into the water column.

- Cyanobacteria and clarity: Samples showed cyanobacteria dominated the phytoplankton during key sampling dates, with Anabaena (a nitrogen‑fixing cyanobacterium) abundant in July and October. Secchi transparency readings were low through much of summer (around 0.5 meter on sample dates), matching the observed thick mats reported by lakeshore residents.

- Seasonal separation of N and P sources: Nitrogen inputs appeared to spike with runoff in winter and early spring, chiefly from upstream watershed flows; phosphorus peaked in the summer when sediment processes and high pH can release bound phosphorus.

- Local observations and stressors: Multiple residents described thick summer algae, shifting winds, beaver and tampering at the outlet structure, and a history of competing water uses and litigation over lake level. A waterfront resident who installed two shoreline aerators said they saw a “night and day difference in water quality starting in May” (Craig, resident). Residents also reported several hundred nearby septic systems in the watershed and ongoing agricultural land use that may move nutrients into Cougar Creek and the lake.

Management options presented

Consultants divided options into near‑term measures intended to reduce available phosphorus in the short run and longer‑term watershed measures to reduce new inputs:

- Short term / local: aeration (circulation bubblers) to prevent nightly oxygen depletion and limit sediment phosphorus release; phosphorus sequestration via alum (aluminum sulfate) or lanthanum‑based products (EutroSorb); targeted algaecide use in high‑risk public access areas. Consultants cautioned that some approaches are temporary and can require repeated treatment and monitoring; they also noted alum can lower pH during application and requires careful Ecology monitoring. Estimated whole‑lake sediment treatment price ranges presented were roughly $115,000 for an alum application and about $122,000 for EutroSorb (consultants’ planning estimates for comparison purposes).

- Longer term / watershed: septic inspection and upgrades, agricultural best management practices (buffers, manure management, reduced fertilizer runoff), shoreline vegetation buffers and public education. Consultants said restoring stream connectivity or off‑channel wetland function in the Cougar Creek reach would be a longer‑term restoration option but that the creek’s incision constrains straightforward constructed‑wetland solutions.

- Wildlife management: reducing year‑round residency by geese and other waterfowl was raised as a potential nutrient‑reduction strategy; consultants noted the available bird‑count data did not allow a precise estimate of waterfowl nutrient inputs and that literature values vary widely.

Community input and technical caveats

Residents reported varied wind patterns and strong localized effects: some said winds calm at night (which would favor stratification), while others described persistent overnight winds. Several speakers described the public‑access boat ramp as a likely place to observe high toxin concentrations because cyanobacterial mats concentrate near shore and at the ramp—matching sampling practice explained by the consultants.

Consultants and staff emphasized data gaps before committing to some interventions: they recommended installing lake‑level staff gauges, more frequent inlet/outlet flow measurements, and short‑term oxygen loggers to confirm whether nighttime anoxia is widespread (a key condition that increases sediment phosphorus release). They also noted the monitoring record covered one year and that additional years would improve seasonal resolution but is not a prerequisite for beginning prioritized actions.

Funding and governance options

Consultants reviewed grant programs and institutional routes for financing work. They described two community governance approaches: a lake association (nonprofit) to lead outreach and some fundraising, and a lake management district created under Washington law (RCW 36.61) that can levy assessments and is eligible for some state grants. Elizabeth Seabacher (independent consultant, formerly Department of Ecology) summarized that the RCW‑enabled lake management district framework is intended for long‑term, ecosystem‑based management and to focus on reducing nutrient inputs.

Next steps

Consultants said a draft management plan would be available for public review in March and announced an in‑person meeting on April 1. They recommended targeted follow‑up monitoring (oxygen loggers, staff gauge, improved inlet/outlet flow data) to refine siting and sizing of aeration or treatment systems before large capital investments.

Ending

The presenters framed the lake plan as a combination of near‑term tactics—to reduce acute public‑health and nuisance risks—and longer‑term watershed and septic solutions to reduce recurring phosphorus inputs. County staff said materials and the meeting recording will be posted to the project website and that the community will have further opportunities to comment before a final plan is issued.