UPDATE 3:45 p.m.:
Environmental health experts say chemicals were in a non-hazardous state and have largely disbursed and diluted. No sulfuric acid reaction. No reports of fish/wildlife kills. Rivers and access sites to re-open shortly.
Citing an "abundance of caution", Montana Fish, Wildlife and Parks Regional Fisheries Manager, Pat Saffel, says the Blackfoot and Clark Fork rivers from Johnsrud Park, west into Missoula are closed down due to a chemical spill.