Mostly by planting emergent native wetland plants around most of the edges, along the stream banks, maybe a few submersed species. Stick with approved natives for that specific region.
I would also pick at it, slowly do say your Sunday chore by planting a little bit each week during the planting/growing season. In 5-10 years, it'll look pretty nice. It's not going to be a fast process.
So contact some of the local groups and see as suggested by others.
I would consider the project on each stream's inflow water quality as a function of the type of plants on each stream. So if you have say 50 ft of sedges, in one stream, and say 50 ft of water cress in another, and the last stream, maybe 50 ft of cattail, then measure the water quality up and down stream flowing into the lake, that might be a good project.
You might test just N and P for example.
Ask the local authorities for $ for or provide the plants, you provide the labor etc, should be a good partnership for both.