Movie star Mark Ruffalo is best known for his big screen roles, but he was checking for contaminated water in the Charles River in Massachusetts on Monday.
Why? The actor founded an organization called Water Defense, which is dedicated to clean water.
Boston's Charles River has been the focus of decades of clean up campaigns, which Ruffalo is now a part of as he films a new movie in the Hub.
He and scientist Scott Smith and Water Defense have a state grant to start deploying indicators for a technique called cumulative testing, which accounts for water contamination over time over the whole water column.
"Today, when they test the river, they come up and they take a bottle, a glass jar, and they scoop a little bit off the top," Ruffalo said. "That only gives you a very minute understanding of what is in the entire water column."
Smith said he compares preliminary draft reports with the cumulative, describing it at as "snap shot."
Ruffalo said he got his passion for clean water growing up on the Great Lakes.
"I lived on Lake Michigan and as a boy, I loved water, like any boy, and I want to swim in the water, but you couldn't swim in that water. It looked clean, but I would see fish with ulcers and tumors swimming by me as a young boy, so I wondered, is that natural? Should that be?" he said.
The actor will be on the Charles and on Cape Cod, where his grant calls for working with the community college there.