FLINT, Mich. (AP) — The Michigan Credit Union League has donated $50,000 in gift cards to Flint residents who are working with officials to monitor lead levels in water in their homes.

Gov. Rick Snyder announced Friday that Flint residents getting the cards live in so-called sentinel sites, locations throughout Flint designated for testing by the Michigan Department of Environmental Quality and the U.S. Environmental Protection Agency.

Snyder says in a statement that it’s a “thank you to residents who have been integral in the testing process.”

Water at those sites is being tested in order to gather data to measure the safety of the water and determine when it is suitable for consumption amid the city’s crisis with lead-tainted water. Data collection at about 600 sites will wrap up in mid-April.