dam

to erect a barrier in a river, stream, brook, etc. We are going to have to dam this stream up to make a pond for the cattle. Let's dam up this stream. Why is this river dammed up?

Fig. past and unchangeable events. Your quarrel with Lena is water over the dam; now you ought to concentrate on getting along with her. George and I were friends once, but that's all water under the bridge now.

if a problem or an unpleasant situation is water under the bridge, it happened a long time ago and no one is upset about it now We certainly had our disagreements in the past, but that's all water under the bridge now.

Also, water under the bridge. Something that is over and done with, especially an unfortunate occurrence. For example, Last year's problems with delivery are water over the dam, or Never mind that old quarrel; that's water under the bridge. These metaphoric phrases allude to water that has flowed over a spillway or under a bridge and thus is gone forever. The first term was first recorded in 1797; the variant dates from the late 1800s.