Range of short‑ and long‑term fixes proposed for Weiser Lake; consultants present sediment capping, aeration and watershed actions

Consultants to Whatcom County outlined a menu of management options for Weiser Lake that combine short‑term treatments and longer‑term watershed actions, but they stressed that additional monitoring is needed to select the right measures and scale.

“Short‑term” lake interventions presented included: phosphorus sequestration (chemical treatments commonly called alum or lanthanum applications), periodic water‑column “stripping” to remove algal biomass, and localized algaecide applications for high‑use areas. Consultants also described aeration — bottom diffusers with shore compressors to mix the water column — as a possible option where nocturnal anoxia is confirmed. Fish removal and goose deterrence were mentioned but not recommended as sole fixes.

Consultants distinguished two treatment modes: lighter annual “stripping” doses applied to bind and remove phosphorus in the water column, and higher “sediment treatment” or capping doses designed to create a binding layer over the sediment. The team said a planning example of repeated annual stripping and buildup could cost on the order of hundreds of thousands of dollars per year; the consultants used a planning‑level example of roughly $311,000 per year applied over 20 years to illustrate long‑term accumulation of binding capacity for both basins (presented as an order‑of‑magnitude example subject to change pending further data and vendor quotes).

Consultants explained tradeoffs: alum (aluminum sulfate) can both bind phosphorus and temporarily reduce pH during application, which helps strip algae from the water column, but it requires pH management. Lanthanum‑based products (marketed for longer‑term phosphorus lock‑up) do not lower pH but are more expensive and generally do not immediately strip algae from the water column. The team emphasized that treating the entire lake may not be necessary; targeted applications to the portions of the East Basin where anoxic sediment release is greatest could reduce cost.

On external controls, consultants urged longer‑term watershed measures — septic system maintenance and upgrades, agricultural best management practices, reduced manure application, riparian buffers and constructed treatment wetlands where feasible — as ways to lower future nutrient load. They noted that watershed fixes reduce reloading of treated sediments over time but can take years to produce visible lake benefits because nutrients in groundwater and soil move slowly.

The consultants also addressed waterfowl: while bird counts are high seasonally, the team said the available bird counts lacked the spatial detail needed to reliably quantify how much phosphorus waterfowl deposit directly into the lake. Literature estimates of waterfowl contributions vary widely; the team therefore did not include a definitive numeric waterfowl loading in the main nutrient budget but listed it as an uncertainty that should be resolved with targeted observation if managers want to consider bird‑management measures.

Presenters repeatedly stressed sequence and combination: short‑term lake treatments can reduce near‑term exposure and nuisance conditions, while watershed investments reduce long‑term loading. They recommended additional monitoring (including nighttime dissolved‑oxygen profiles and spatially distributed sediment assessments) to determine whether aeration or sediment capping should be applied across all basins or only in strategic areas.

No formal decisions were taken; consultants provided these options for community review and for grantor/agency consideration.