Great Seneca Creek Record

Road salt reaches the creek every winter

Watch Chloride in the creek climbs from about 85 mg/L in summer to winter peaks of 159, still below the EPA's 230.

159 mg/Lhighest winter chloride in the creek
132 mg/LMaryland Salt Watch median

Since 2024 the chapter has tested its creek and lake for chloride with Salt Watch strips.

Road salt dissolves in meltwaterStorm drains carry it straight to the creekGreat Seneca CreekNa+Cl−Na+Cl−Na+Cl−Na+Cl−Na+Cl−Na+Cl−Na+Cl−not to scaleInsects keep salts in balance through their gillsEPA limit 230winter peak 159MD median 132summer 85Chloride, mg/L
Illustration of the path; the gauge uses the chapter's readings. The gill and ions in the lens are drawn far larger than true.
Salt Watch chloride readings from the chapter's own sampling points. Dashed line: EPA chronic aquatic-life criterion for chloride, 230 mg/L.

Road salt shows up every winter: winter peaks were 2024–25: 145, 2025–26: 159. All readings so far sit below the EPA's chronic aquatic-life level of 230 mg/L and below the Maryland Salt Watch median of 132 mg/L.

Two winters is too short for a trend; more years will show whether the peaks keep rising. Salt is a likely suspect for the loss of sensitive animals, since mayflies and stoneflies are among the first to suffer.

Related