Get Full Government Meeting Transcripts, Videos, & Alerts Forever!
Get email alerts on the Environment Water topic
No spam. Unsubscribe anytime.
Kenmore seeks aeration and targeted treatments as cyanobacteria and invasive plants appear along shorelines
Summary
City staff and consultants recommended installing aeration at the lagoon by Tawquharis Park and continuing a combination of mechanical, herbicide and monitoring work at Logboom Park and Arrowhead Point after recent algae and plant growth and citizen-sampled toxins were found.
Kenmore's Environmental Services director and consultants gave an update on aquatic vegetation and harmful algal blooms at city shorelines and recommended a mix of short- and long-term measures including aeration, targeted algaecide/phosphorus-inactivation treatments, mechanical skimming and expanded monitoring.
Richard Sawyer, the city's environmental services director, told the council the city's ongoing aquatic vegetation management has relied on diver-assisted suction dredging for small-scale removal and shore raking, but those methods are costly and scale poorly for larger open-water areas. Staff and Herrera Environmental recommended early-season herbicide treatments targeted at Eurasian watermilfoil and a second broader treatment later in the season for nuisance plants in expanded treatment areas at Logboom Park.
At Tawquharis Park's lagoon (fed by Swamp Creek), consultants recommended a longer-term aeration system to raise dissolved oxygen and reduce episodic filamentous algae and toxic cyanobacteria (blue-green algal) blooms. Rob Szyszet, Herrera's principal aquatic scientist, said the lagoon is nutrient rich, poorly circulated and prone to low oxygen; aeration is less costly over a ten-year horizon than recurring chemical treatments and would be the preferred long-term solution. Short-term mechanical skimming and selective algaecide/phosphorus-inactivation treatments would be used as needed while aeration is implemented.
Arrowhead Point and the river mouth: City-funded monitoring and a consultant survey found elevated chlorophyll and cyanobacterial pigment concentrations along the river mouth and nearshore areas; microscopic analysis confirmed cyanobacterial taxa among samples. Herrera recommended additional targeted sampling and species-level lab analyses over a multi-event winter season (estimated cost $35,000 to $60,000) to determine whether shore blooms originate from pelagic lake populations, benthic sediments, aquatic plants or riverine inputs.
Public comment and council response: Several residents thanked the consultants and requested extended monitoring and improved communication. Staff supported citizen observer programs and regional coordination, noting the dynamics are lake- and river-wide and King County or regional partners could add scale to any monitoring and remediation. Staff also said they will coordinate treatment timing with park events to reduce public disruption and will continue weekly bacterial testing during the swim season.
What happens next: Staff will pursue design and procurement for aeration at the lagoon, continue seasonal raking and skimming, schedule targeted herbicide/algaecide treatments through licensed applicators, expand monitoring where feasible and explore citizen-observer programs and regional cooperation.
