Today I rescued a turtle that was having some trouble from a river near my house, what should I do now? How should I take care of it?

Today I spotted a turtle that was having trouble getting out of the river next to my house, it was swimming against the current and falling over every time it tried to get out; so I took her home while deciding what to do with it. His/her shell is a little bit broken on one side (part of it is lifted). I don't know anything about turtles and this one is quite big (about 15inch/40cm in length). Does anyone have any advice? I am doubting if it was a good idea to take her out of the river, but I'd rather know better before returning it since it looked like she wasn't comfortable there. Right now I am keeping it inside a washbasin with water. Any suggestions? Thanks!