It was a fine summer morning when Dave Nelson steered his small airplane into bright-blue skies and guided its nose toward Lake Pepin.

From above, the swell of the Mississippi River gleamed navy brown, pierced occasionally by the white wake of a pleasure boat. But on closer inspection, Nelson pointed out lime-green patches of algae surreptitiously skimming the lake’s edges and tributaries.

The flight wasn’t taken for pleasure. Nelson was on a mission for NASA.

The Rochester resident, a retired engineer from IBM, is one of a handful of private pilots nationwide scoping waterways from the skies for toxic scum. In Minnesota, the idea is to track and document harmful algal blooms in the Mississippi River — the source of drinking water in Minneapolis, St. Paul and several other communities in the Twin Cities.

Once a week, Nelson attaches a tiny camera to the wing of his four-seat plane, which he built in his garage. To ensure consistency, he guides the aircraft on the exact same route, from the southern end of Lake Pepin south to La Crosse, Wis., about 2,000 feet above the river, shooting photographs along the way.

“As the summer goes on, it gets worse,” Nelson observed, while peering from his plane at a bright-green patch. “It looks like you could walk on it.”

The footage is uploaded from the camera, which he controls with his smartphone, and sent to NASA’s John H. Glenn Research Center in Cleveland.

There, Rafat Ansari, a scientist and principal investigator with NASA’s citizen-science program, gathers the data and posts it on a public website hosted by Cleveland State University for use by researchers, students, teachers, nonprofit organizations, water quality managers and others.

Ultimately, Ansari hopes the information will help monitor and possibly forecast harmful algal blooms coast to coast. NASA also compares the photos gathered by the pilots with data culled from satellites tracking algae in space.

Algae — a diverse group of simple, plantlike organisms that float on or close to the surface of water — serve as an important food source for aquatic life. Algae feed on phosphorus, a key ingredient in manure, farm fertilizer and sewage.

Under the right conditions, potentially harmful algal blooms can emerge from the scum. The National Oceanic and Atmospheric Administration (NOAA) calls these blooms “tiny plants with a toxic punch.”

“Not all algae is bad algae,” Ansari said. “Algae is a big factor in fish and aquatic life. It is the toxic algae that is harmful, that’s what we can see from the airplane.”

NOAA says these blooms are on the rise, and should be considered a national concern because they affect not only the health of people and marine ecosystems, but the health of local and regional economies, as well.

That’s kind of how Ansari got involved in the NASA program.

A smell on Lake Erie

A private pilot himself, Ansari and his wife, Surryia, flew one afternoon a few years ago to Lorain County along the Ohio shore of Lake Erie. “My wife indicated that the water looks very, very green,” he said. “We parked the plane and went for lunch at a restaurant close to the lake. There was a lot of odor, and there were signs on the beach saying it was not safe to swim in the water because the bacterial count was very high.”

Ansari is not a biologist. His specialty is “biomedical optics, optical, photo-optical, optoelectronic applied science and experimental ophthalmology,” according to his NASA bio. But at a scientific conference a few years later he saw pictures of algal bloom. “That’s exactly what I’ve seen in my airplane,” he thought. And the idea of his citizen air patrol was born.

It’s not unusual for government to partner with volunteers on research studies and projects. The Minnesota Department of Natural Resources, for example, has used volunteers to help it track Minnesota’s moose population.

But this effort has more of a grass-roots feel. Ansari signed on with Cleveland pilot Terry Schubert, and the two friends started surveying Lake Erie, relatively shallow when compared with the other Great Lakes. In shallower swells, harmful algae can thrive, as was the case in 2014 when a toxic bloom shut down Toledo’s water system.

Schubert and Nelson are friends through experimental aircraft circles. And so a small but determined pilot posse was formed. Two other pilots are surveying waterways in the San Francisco area, and another is flying in Pennsylvania.

Private planes can fly relatively low, below the clouds, making them perfect tools for surveying.

But NASA cannot afford to pay legions of private pilots for this work or the $300 camera. The citizen pilots pay for their own fuel and the use of the aircraft.

A commitment to science

Nelson says he got involved because he feels a deep commitment to furthering science. He’s not interested in leveling blame against farming and other industries often blamed for the blooms. Nor does he want to get into a philosophical debate about climate change.

As a career engineer, “I’m a big believer in data,” he says. “I don’t see this as political.”

Besides, Ansari notes, pilots are always looking for an excuse to fly, even to another airport just to eat lunch. “They call it the $100 hamburger,” he jokes.

Recently, Ansari and Schubert penned an article for a magazine published by the Experimental Aircraft Association describing their project. More than 100 pilots from across the country responded, ready to take off and survey their own lakes, rivers and waterways.

“What surprised me is the devotion and dedication of the pilots,” Ansari said. “They already know they’re not getting anything out of it. That really is the spirit of aviation, and that spirit is alive and well.”