As Rebecca Miller waded into Mashpee’s Santuit Pond, mesh plankton net in hand, a vacationing couple walking a pair of dogs was retreating from the shoreline. Like Miller, Matt Eastman and Alexis Parr are biologists, so they knew the importance of pulling the dogs back when they approached the pond’s gently lapping waters. “Benni just tried to drink the water and I made sure to tell him not to,” Eastman said of the couple’s schnauzer mix. “I heard on the local news in Connecticut that with all the rain there are high bacteria levels.” Eastman’s instinct was spot-on.