Satellites do an incredible job of mapping algal blooms, the green mats that spread over lakes and oceans during warm, nutrient-rich summers. But the hypnotic, swirling images from space can't tell if toxins are lurking in a carpet of cyanobacteria, threatening the safety of water. Ecologists and hydrologists can test water's drinkability by boating through the blooms--though collecting samples off the side of a power boat is tricky and inconvenient. So this year, scientists are monitoring Lake Erie with a robot, 18 feet below the water's surface. The so-called Environmental Sample Processor, ESPniagara, sits on the floor of Lake Erie's western basin.