Saving tadpoles (1)

There’s a little body of water near my building in New York where, a couple months ago, my kids an I found a few hundred tadpoles. The water was bright blue and beautiful and the tadpoles, big, and always swimming around full of life. Over time, the water has gone more gray, and the tadpoles move around a lot less, some don’t seem move at all. Are they hurt? Can I help them?  Jenna