Three Florida residents have filed a lawsuit against Mosaic Co. that seeks to hold the fertilizer company responsible for potential contamination of their drinking water wells after a 45-foot-wide sinkhole opened at one of its plants, releasing wastewater into an underground aquifer.

Mosaic said last week the massive sinkhole had opened up at its New Wales facility, which produces fertilizer and ingredients for animal feed from phosphate rock. Millions of gallons of contaminated water spilled toward the Florida aquifer that...