I had a customer call me up this morning worried about the rain getting in her pond. After we hung up I realized this might be a concern to other people. The rain poses no threat to your pond in general. If your pond is constructed properly with an overflow point of some kind . This can be as simple in some ponds as a low spot on the edge designated for this pourpose, most professionally installed ponds will have a pipe somewhere that will drain off the water when it reaches a certain height. Another concern would be contaminants being entroduced into the pond with the rain. In some areas smoke,ash, or chemicals could be washed into your pond, but in the Southern California area this isnt a problem, however if a drain or run off from gutters alows water to get into the pond , contaminants from these sources can be extremely damaging. Most of these contaminants are either roof debri or sedimant that normally sat in one place only to be washed into your water course. But with a little attention to these few spots the rain will be a tast of fresh water to your pond.