Experts say rain is Spa Creek’s main water‑quality driver; signage and targeted testing recommended

Amy Clemens of the Spa Creek Conservancy and Tammy Deansky of the Anonda Community College Environmental Center told the Environmental Matters Committee that ten years of monitoring across Spa Creek and Back Creek show rainfall is the principal driver of most water‑quality spikes.

“The takeaway is really the rain,” Clemens said, explaining that many 2025 sampling days coincided with heavy or recent precipitation and that geometric‑mean calculations are used to smooth extreme single events. She and Deansky described a network of shoreline and midstream sites from headwaters to the mouth and said concentrations at shallow headwater sites often rise sharply after rain.

Why it matters: elevated bacterial counts and suspended solids reduce water clarity, can promote algal growth and may lead to localized low‑oxygen conditions that stress aquatic life. Presenters noted that the geometric‑mean threshold used for some assessments is 35 colony‑forming units per 100 milliliters and that many sites exceeded that value in 2025 when sampling fell soon after storms.

Key findings and evidence: the presenters said that, while nutrients (total nitrogen and phosphorus) and algal indicators sometimes spike after rainfall, they did not point to a single dominant chronic sewage source. Past attempts at bacterial source‑typing with a private contractor produced poor results; presenters called for higher‑quality, costlier testing (and possible collaboration with the Smithsonian Environmental Research Center) and suggested wildlife camera surveys in headwater areas where animal activity may be concentrated.

Alderman Huntley asked whether any parts of the creek are safe to swim in the day after rain. “The guidance will always be: don’t swim for a day to two days after it rains,” Clemens said, while noting that midstream areas with greater dilution often return below thresholds faster than shallow headwater sites. Committee members and staff discussed posting clearer signage in English and Spanish at parks and informal access points and refining public messages to recommend avoiding contact within 24–48 hours after rainfall.

Restoration context and next steps: speakers pointed to places where restoration has been followed by improving trends (for example, Hawkins Cove) and outlined upcoming projects (a submerged gravel wetland and a neighborhood rain‑garden) that will carry before‑and‑after monitoring. Presenters urged the city to fund or co‑fund rigorous source‑typing so outreach and actions can be targeted rather than broadly applied.

The meeting record: presenters concluded by reiterating that many measures improved in dry periods and that a combination of signage, continued monitoring, targeted source testing and prioritized restorations offers the best path forward. The committee did not take formal action; staff agreed to follow up on signage options and potential funding for higher‑quality source analysis.