Cassie Guy, left, and Katelyn Roberts, both fifth-graders at Shapleigh Middle School in Kittery, react as a horseshoe crab wiggles its tail Friday at the Explore a Marine Tidepool exhibition, part of the 16th annual Southern Maine Children’s Water Festival at the University of Southern Maine in Portland.

The festival — organized by a partnership that included the Maine Department of Environmental Protection, Portland Water District and Poland Spring — welcomed 650 fourth-, fifth- and sixth-graders and their teachers from 15 regional schools to learn about clean water, wetland ecosystems and the importance of protecting Maine’s hydrological resources.