# Cyanobacteria river blooms causing dog deaths > Live situation record from CLSTR: https://clstr.news/situations/cyanobacteria-river-blooms-causing-dog-deaths > Updated: 2026-07-31T11:30:28.000Z. Sources: 4. Developments: 2. In late July 2026, U.S. health officials issued a warning after a dog died of liver failure linked to a suspected benthic cyanobacteria bloom in a stretch of the Charles River in Massachusetts. The advisory urged the public and pet owners to avoid the water and shoreline while water samples were collected for toxin testing. A few days later, French authorities reported a massive cyanobacteria bloom spreading downstream from Chazey‑sur‑Ain to the confluence of the Ain and Rhône rivers. The bloom was associated with several recent dog fatalities across multiple regions, prompting officials to advise the public to stay away from discolored or foamy water and to keep pets from drinking or swimming in affected areas. Both incidents highlight the growing risk of toxic algal blooms in temperate rivers during warm conditions and the resulting public‑health advisories aimed at protecting humans and animals. ## Timeline ### 2026-07-31: Cyanobacteria blooms in French rivers cause dog deaths, authorities urge caution Cyanobacteria blooms in French rivers have killed several dogs; officials warn owners to keep pets away from contaminated water and follow safety signs. 2 sources. https://clstr.news/cluster/cyanobacteria-blooms-in-french-rivers-cause-dog-deaths-authorities-urge-caution ### 2026-07-26: Massachusetts warns of possible toxic algae in Charles River, advises public and pets to avoid water Massachusetts health officials warn residents and pets to avoid a Charles River stretch after a dog death possibly linked to a hidden cyanobacteria bloom; testing results are pending. 2 sources. https://clstr.news/cluster/massachusetts-warns-of-possible-toxic-algae-in-charles-river-advises-public-and-pets-to-avoid-water --- Cite as: Cyanobacteria river blooms causing dog deaths. CLSTR, https://clstr.news/situations/cyanobacteria-river-blooms-causing-dog-deaths