How can I help this baby bird?

Today I grabbed a baby red-winged blackbird out of the river.It was a fledgling and it must have fallen in as it tried to leave the nest.I watched it “paddle” with it’s wings to get close to shore where I was able to grab it.I nailed a plastic container with drain holes to a tree and filled it with grass.What do I do now??
I know there are one’s that would say to let nature take it’s course,but this little guy tried so hard to make it to shore that I want to give it a fighting chance.Does anyone know what I can do for him?