LINCOLN, Maine — When people talked about fish kills or reductions in aquatic life in Maine’s rivers, lakes and streams, Catherine Chan didn’t think much of it.

Then the 22-year-old Lincoln resident and Boston College graduate spent from late June to early October examining culverts for T he Nature Conservancy and learned just how tough some fish have it traveling through rivers and streams for places to spawn or eat, she said.

“A lot of times people would tell us that years ago, there were a lot more fish, like brook trout,” Chan said earlier this week, “but now it seems that the streams dry up and there is some type of barrier or lack of rainfall that keeps them away.”

“Basically all fish need places to migrate to, whether into saltwater or in freshwater,” Chan added, “but even for brook trout, a lot of rivers weren’t connected. If they only have a small portion to migrate around in, then it is not really effective for them.”

While northern Maine doesn’t lack for fish habitats, the state does have a considerable deficit in well-maintained, environmentally sensitive culverts, or supports built under roadways that help convey water from streams to rivers, said Josh Royte, a conservation planner with the conservancy.

For seven years, the conservancy has been sending individuals such as Chan out during summers to measure culvert efficiency and target those that are too narrow, or rotted away, to allow for fish passage, Royte said.

“What we want is for streams to act like streams, where there is a natural bottom, where sediment can go through it and culverts match the angle of the stream and slope so that you get an even passage of the water that doesn’t speed it up too much,” Royte said.

Many fish can’t swim upstream against culverts that significantly speed water flow or sharply angle streams, Royte said. In the seven years, conservancy workers have inspected about 15,000 culverts out of 25,000 to 30,000 in Maine. The workers’ reports form the basis of plans to repair or replace culverts that inhibit fish migration, Royte said.

Chan spent her time inspecting culverts in the Downeast Watershed from Blue Hill to Cherryfield, taking about 25 measurements per culvert, he said.

“We definitely saw lot of things that didn’t seem adequate for passage,” Chan said. “A lot of time they haven’t been maintained really. Some of the things we would see were just rusted out metal culverts. It was very concerning.”

The conservancy is working with state and local officials to ensure that replacement culverts are designed and installed well enough to avoid blocking fish passages, Royte said.

He knows of at least 30 projects around the state on public and private roads where culverts will be replaced with larger open-bottom structures like arch-culverts or bridges over the next year to improve wildlife habitat and protect the stream and road network, he said.