We describe a collaboration between mathematicians and ecologists studying the cyanobacterium "Gloeotrichia echinulata" and its possible role in eutrophication of New England lakes. The mathematics includes compartmental modeling, differential equations, difference equations, and testing models against high-frequency data. The ecology includes observation, field sampling, and parameter estimation based on observed data and the related literature. Mathematically and ecologically, a collaboration like this progresses in ways it never would have if either group worked alone.