They don't build many dams here in E Texas that look like the traditional beaver dams up north...don't build the same type lodge as their Northern cousins either. If ya don't know what to look for, you'll never know they're there. They tunnel into the steep banks under the water, go upwards to above normal water level, make several compartments, and the tunnels can go out into the side of the bank a long ways, with openings that look like a rabbit hole. I've dug several out with my backhoe..they can be extensive.
My little river would be called a creek most times and it's full of them, without a single dam anywhere, but if you know what to look for or listen close at night, you can hear them. The juveniles like to play and splash around. We get too much torrential rain here for a traditional stick dam to hold in place when the water gets into flood stage. They're happy enough in the river, using the deep pools that usually occur in bends of the channel instead of trying to dam up the flow.
The dams they do build here are almost always mud and grass, and if not torn out soon, will grow over with grass and brush and you'd think it's just a natural buildup of dirt and grass and brush. When they build those, they're like little bulldozers, pushing the aquatic grass and mud along in front of them in their front paws and into the dam base and top. They go out into the grassy areas near their tunneled lodges and gather or cut grass and leaves to line the nursery part of their lodges.
They will clog up drain culverts if they have to tho..had a pair do it several years ago.
Might take a picture of a dam that has been under construction for about 2 months now. Getting wider at the base, longer accross and higher all the time. Wide enough now that cows are walking on it.