Chehalis River

• Discharges affecting the Chehalis River in Washington, last 12 months11 affecting this stretch: 1 reported on the Chehalis River; none arriving from upstreamDecember 2025 to November 2026Verified reports where available, else notices; revisions and duplicates counted once. Arriving discharges are estimated from modeled downstream reaches.
• Days with a discharge affecting the Chehalis River in Washington, last 12 months1Reported on the Chehalis River in Washington: 1 · Arriving from outfalls upstream, estimated: 0 (counted apart; together they need not equal the total)December 2025 to November 2026A day counts once however many discharges were under way on it.
• Hours with a discharge or advisory status on the Chehalis River in Washington, last 12 months2Reported on the Chehalis River in Washington: 2 · Arriving from outfalls upstream, estimated: 0December 2025 to November 2026Red hours by the map's rules: each discharge to its reported end plus the state's post-discharge period; overlapping hours count once.
• 2026 season with a discharge or advisory status on the Chehalis River in Washington0.1%May to October 2026; incomplete source coverageShare of May 1 to October 31 hours with red status by the map's rules, of the hours a source covered.
• Records behind the last-90-days strip for the Chehalis River in Washington1Reported on the Chehalis River in Washington: 1 · Arriving from outfalls upstream, estimated: 0last 90 daysEvery distinct record the strip lists for its red, yellow and unresolved hours, notices and unresolved reports included; counted as the strip counts them.

Combined sewer overflow (CSO): sewage mixed with rainwater spills from a shared sewer system. Sanitary sewer overflow (SSO): sewage spills from a sewer meant to carry sewage separately from rainwater. Treatment bypass: wastewater skips one or more treatment steps. Blended discharge: wastewater that skipped some treatment is mixed with treated wastewater. Outfall: a pipe or outlet where wastewater enters a water body.