Earth bottom pond

Question
I have an earth bottom pond that's around 15' x 30'.  When we have rain, there's quite a bit of runnoff from the surrounding landscaping.  And we have lots of trees and leaves that regularly fall in.  

After each rain, the pond becomes the color of very strong tea - which, I imagine, is buildup of tannin from decaying leaves.

Is there something I can do to fix this?  

We have goldfish and other fish that I'm sure the condition is harming.

Answer
Hey Christine, the only thing I can think of is the same thing that farmers do to there farm ponds.Every so many  years say 10, they have to get a back hoe and dig it out. You need to clean it out. Maybe rent a small back hoe. It will eventually fill in. Thanks Eric