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. It collects algae from the surrounding water, analyzes microcystin (a small, circular liver-toxic protein), and uploads results for researchers at the end of every test. They're watching this toxin closely, because elevated levels of it could swiftly poison the water supply for humans and wildlife in the surrounding area.

A no-frills charm dominates the ESPniagara's aesthetic. “It kind of looks like a trash can,” says Tim Davis, a molecular ecologist at NOAA in Ann Arbor. Tentacles of clear plastic tubing for sample processing swirl around the lab-in-a-can’s lower half, while circuits and wiring snake between the components above. Those electronics and the machine’s batteries—400 D cell batteries power the unit—understandably need some protection to sit at the bottom of the lake. “The metal trashcan is essentially a pressure case that can withstand very, very high pressures, and essentially keeps it dry,” Davis says.

Staying dry isn’t the only requirement for the lab capsule. ESPniagara also needs to stay put, remain upright, and avoid sinking too deeply into the gunky mud. So NOAA recruited applied physicists at the University of Washington to design the 1,000-pound frame encasing the unit. By their calculations, even if Hurricane Sandy-level winds hit Michigan, the water sampling could continue. And at the lake’s surface, a round orange data buoy relays information from its tests via a cellular modem, like the one in your phone.

So far ESPniagara has been testing the water every other day. But as of August 1, with the risk of harmful blooms steadily rising, it began testing on a daily schedule. It pulls lake water in, concentrating algae cells onto a filter. When the filter is clogged with plenty of algae to measure, the biology begins.

An algae bloom in western Lake Erie, July, 2015. NASA

While full-scale labs use temperature-controlled water baths, freezers, and centrifuges to run these kinds of experiments, the ESPniagara accomplishes the same tests with a few carefully formulated protocols. Each toxicity measurement happens within a quarter-sized puck that’s about an inch and a half tall.