California water regulators roll out updated benthic cyanobacteria monitoring guidance, set 15% cover posting threshold

State Water Resources Control Board staff on a May webinar introduced revised guidance and a field standard operating procedure (SOP) for monitoring benthic harmful cyanobacterial blooms (HCBs), including interim numeric thresholds and a tiered monitoring approach using solid-phase adsorption toxin tracking (SPAT).

Hannah Merges, a California Sea Grant fellow placed with the State Water Resources Control Board’s Office of Information Management and Analysis working with the SWAMP unit, said the updated guidance sets a visual percent-cover threshold of 15% for posting a yellow “toxic algae” advisory: “Anything above that 15% cover is gonna trigger a signage posting,” Merges said during the presentation.

The guidance updates standardize three monitoring types — event response, follow-up monitoring and routine monitoring — and prioritizes rapid, low-cost percent-cover visual assessments for immediate posting decisions. The tiered approach uses SPAT samplers as a first pass (deployed roughly four to seven days), followed by visual inspections and composite mat sampling for toxin and taxonomic analysis if indicators warrant it.

Elena Solia, an environmental scientist in the Office of Information Management and Analysis, walked attendees through the field SOP for in‑water and shoreline assessments, including how to define a sampling reach, record spatial coverage and collect a composite mat sample. The SOP directs teams to sample a maximum 50-foot reach, collect a composite of roughly twelve 3 cm × 3 cm mat pieces from four hot spots (two in water, two near shore for flowing channels), and place samples in amber glass jars for shipping.

The SOP includes operational details intended to reduce barriers for monitoring groups with limited resources: simple equipment lists, a two‑person recommended zigzag survey pattern for flowing channels, and a printable field data sheet with diagrams for estimating percent cover. Solia said the protocol is designed to be implemented without specialized equipment and that resources such as a two‑page cheat sheet and a visual genera guide will be distributed.

On evidence management, presenters advised specific handling and shipping steps: keep samples on ice (2–8 °C), do not freeze, ship overnight where possible, and note that lab hold time for received samples is five days. The guidance also recommends contacting the receiving lab ahead of shipment to coordinate timing and paperwork.

Merges noted that earlier statewide guidance (the 2017 benthic SOP and a 2020 voluntary CCHAB guidance) had encouraged posting on any cyanotoxin detection and that public feedback from some regions showed “sign fatigue” and economic impacts from frequent postings. The updated approach aims to reduce unnecessary postings by combining rapid percent‑cover observations with SPAT and toxin data to refine posting decisions.

The revised signage set remains two tiers (a green awareness sign and a yellow toxic‑algae advisory) and will be available in English and Spanish; signs include a QR code and a field to indicate the posting date. The guidance recommends biweekly observations of posted sites and follow-up monitoring if visual conditions change.

Presenters emphasized that percent‑cover assessments do not substitute for toxin analyses: percent cover provides rapid field information for immediate public‑health decisions, while lab‑based toxin analyses (ELISA, qPCR, SPAT analysis) inform follow‑up and longer‑term actions. The guidance is described as interim and iterative; staff said thresholds and procedures will be updated as additional science becomes available.

The webinar closed with a question-and-answer period; staff encouraged voluntary participants to notify the Water Boards when they post signs so postings can be reflected on a statewide map and to use the Cyanohab reporting email for questions and reports.