DULUTH – In some ways, Todd Carlson was like a detective who cracked thousands of cases involving crimes against the city's lakes, rivers and streams.

Sometimes erosion was the culprit, filling up the beds where the trout like to spawn. Other times washed-away road salt ratcheted up chloride levels, a potential danger to aquatic life. Particularly bad storms even caused untreated wastewater to overflow the sewage system and run into creeks.

"I always tell people one of the tricks is: Follow your nose," said Carlson, who retired last week after 21 years working for the city of Duluth, most of which were spent as program coordinator in the municipality's engineering department.

His favorite part of the job — which he called "the best career in the world" — wasn't being the environmental Sherlock Holmes. Carlson enjoyed helping educate the public about pollution and drainage even more.

"In a city as large as ours, with as many creeks and streams as we have, if we don't have the public's eyes out there looking, we can't see everything," Carlson said.

The 55-year-old grew up on the east side of Duluth and spent many of his childhood summers exploring the outdoors. For two years as a young adult he led Boy Scout trips to the Boundary Waters and Quetico Provincial Park in Canada. Then he spent 15 years as an assistant golf course superintendent at Northland Country Club.

Carlson joined the city in 1999, after a neighbor told him it was a great place to work. He started out working as a maintenance worker, using machinery to clean out sewers, dig pipes and make repairs to the system.

Starting in 2003, cities were required to follow new stormwater regulations that prohibited the discharge of pollutants into U.S. waters. Duluth was fined and ordered by federal officials to stop millions of gallons of sewage from seeping into Lake Superior and the St. Louis River during heavy rains.

Carlson was a key part of the team that worked to improve infrastructure and drainage systems. In 2015, Duluth was one of the first originally problematic cities to receive a stamp of approval for its cleanup efforts.

"Todd left this city cleaner than he found it," said Jim Benning, Duluth's director of public works and utilities.

Over the years, Carlson has made countless house visits to examine residents' problems with their sewers or drains. He remembered a time recently when a trio of neighbors called because their yards kept flooding. Carlson promised to use city funds to build an inlet near the properties if the homeowners could work together to install a French drain, which they threw a mini block party to celebrate.

"It's not stuff that the average person gets super excited about," said Cindy Hagley, who worked with Carlson while she was the environmental quality extension educator for Minnesota Sea Grant. "Todd had a way about him, making it really fun and understandable."

Over the years, Carlson worked with a regional team on public awareness campaigns about grass clippings, leaf litter, salt runoff and sump pumps. He recently helped launch Duluth's push to get owners to pick up after their dogs with ads saying: "There's no poop fairy to do that for you."

"He was always looking for inventive ways to reach people," said Lucie Amundsen, who collaborated with Carlson through her role as public information officer for the Minnesota Pollution Control Agency in Duluth.

Carlson is looking forward to spending a lot more time at his cabin an hour north of Duluth. But he and his wife will continue to live in the city, next to the maze of waterways he knows so well.

"Duluth is unique because I can drive five minutes and the city disappears. The waters are bubbling, the birds are chirping, the sounds are gone," he said. "It's just this little slice of nature I think people need to really reconnect with who they are."