New fish I didnt put in my pond

Question
I moved into a new house with beautiful pond and waterfall 2  years ago.  20
goldfish have been thriving.  Last summer I noticed 2 different fish in my
pond that were brown in color.  They are about half the size of my goldfish
(which range from 5-8 inches.  Last week I counted 9 more of these little
brown "tramp fish" about 1 inch long.  I have bought no new water plants
since purchasing the property.   I live approximately 5 air miles from the
Allegheny River in Pittsburgh.  There have not been any ducks in my pond,
but other birds splash in the marsh area above the waterfall.   Where do you
think these invaders to my pond are coming from and should I get rid of
them?  

Answer
Hi Grace!
Hard to tell for sure what they are without seeing them, but...Goldfish hatch dark brown/black and turn into their orange color as they mature. Some sooner, some later.
That being said, it is absolutely possible that some other fish eggs got into the pond on plant roots or bird feet.
Keep your eye on them and see what they develop into ;-))