dam

(as) busy as a beaver (building a new dam)

Very busy, assiduous, or hardworking. The phrase refers to beavers' reputation for being extremely industrious. Between working two part-time jobs, volunteering on the weekends, and looking after his little brother, Sam's been busy as a beaver this summer. I've been as busy as a beaver building a new dam this year. I've had almost no free time!
See also: beaver, busy, new

an ant may well destroy a whole dam

proverb A small problem can cause catastrophic damage if left unchecked. A: "I can't believe that minor leak totally rotted the floorboards in here." B: "Unfortunately, an ant may well destroy a whole dam."
See also: ant, dam, destroy, may, well, whole

dam up

To block something from flowing freely, typically water in a stream, river, etc. A noun or pronoun can be used between "dam" and "up." If we don't dam up the river, this rain will cause a flood.
See also: dam, up

water over the dam

A prior issue or unfortunate past event that is now considered resolved, settled, or forgotten about. That argument we had is just water over the dam now—don't even worry about it. A: "I'm so sorry for bringing up that thing with your father again!" B: "Don't be, that was a long time ago. It's water over the dam."
See also: dam, over, water

water under the bridge

A prior issue that is now resolved or considered resolved. That argument we had is just water under the bridge now—don't even worry about it.
See also: bridge, water
Farlex Dictionary of Idioms.

dam something up

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?
See also: dam, up

water over the dam

 and water under the bridge
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.
See also: dam, over, water
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

water over the dam

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.
See also: dam, over, water
The American Heritage® Dictionary of Idioms by Christine Ammer.

water under the bridge

BRITISH, AMERICAN or

water over the dam

AMERICAN
If you say that a bad experience is water under the bridge, you mean that it happened a long time ago and so you do not feel upset or worried about it now. He didn't treat me very well at the time but it's all water under the bridge now. Mr Bruce said that he was relieved it was over and that he regarded his time in jail as water under the bridge. Note: You can also say things such as a lot of water has gone under the bridge to mean that a lot of time has passed or a lot of things have happened since a bad experience. It's almost two years since it happened and a lot of water has gone under the bridge. We're now on speaking terms with Marcia.
See also: bridge, water
Collins COBUILD Idioms Dictionary, 3rd ed.

water under the bridge

used to refer to events or situations in the past that are no longer to be regarded as important or a source of concern.
The related expression there's been a lot of water under the bridge since — is used to indicate that a lot of time has passed and a great many events have occurred since a particular event. A North American variant is water over the dam .
See also: bridge, water
Farlex Partner Idioms Dictionary

water under the bridge

A past occurrence, especially something unfortunate, that cannot be undone or rectified: All that is now just water under the bridge.
See also: bridge, water
American Heritage® Dictionary of the English Language, Fifth Edition.

water over the dam

Over and done with; past. This term, along with the slightly older water under the bridge, is a metaphor for anything finished and irreversible just as water that has once flowed through a spillway or under a bridge is gone forever. Richard Sale combined both metaphors in Passing Strange (1942): “‘That’s water under the dam.’—‘Bridge,’ I said. ‘Or water over the dam.’”
See also: dam, over, water
The Dictionary of Clichés by Christine Ammer
See also:
  • (as) busy as a beaver (building a new dam)
  • beaver
  • building
  • busy as a beaver
  • busy beaver
  • busy little beaver
  • work like a beaver
  • work like a Trojan
  • I don't have time to breathe
  • I don't have time to catch my breath
References in periodicals archive
Kenya will need Sh440 million to improve the safety of its hundreds of dams over the next three years.
It also entails setting up of State committee on dam safety and State Dam Safety Organisation.
Mujahid Saeed said a total of 25 small dams were so far completed in KP, adding 18 were completed including nine each under ADP and PSDP after 2003.
NIA-UPRIIS made the assurance following the initial post-earthquake assessment of seven major dams in the area after the temblor, Bote added.
The meeting was also informed that the construction of 100 small dams in Balochistan was based on five packages.
Interestingly, the government, through the Ministry of Agriculture, has stocked the dams in Maragua with over 55,000 fish fingerlings in a move aimed at boosting fish farming in the county.According to Mr John Mwangi, the Fisheries Director in Murang'a South, the stocking will boost the community surrounding the dams and will encourage them to protect the dams from encroachment.
style="font-weight: 400The ex-CJP assured people's donations would be spent only on the construction of dams. style="font-weight: 400Speaking on the occasion, PTI Senator Faisal Javed Khan said he wanted to make it clear that dams would certainly be constructed in the country.
'With this amount of Rs7 or 8 billion, collected under fund-raising drive, you cannot make big dam, however it can help construct enough small and medium sized dams in Balochistan,' said Senator Usman Kakar during the meeting of the Senate Standing Committee on Planning, Developments and Reforms.
R A W A L P I N D I -- Punjab government has decided to utilize 3 mini dams including Misriot dam, Khasala dam and Jawa dam located near Dhamial and Adiala to supply water to citizens of Rawalpindi.
There has been an impassioned debate on the controversial Kalabagh Dam in the country.
Mr Ejaz, who is the coordinator of the Pakistan Network for Rivers and Dams and president of the Social Organisation for Mutasireen Tarbela Dam, told reporters here that the announcement of the Supreme Court chief justice and PTI government for the construction of Diamer-Bhasha and Mohmand dams was a welcome move and that it should be supported in the country's best interest.
Pakistan Peoples Party (PPP) on Monday submitted resolutions against the dam in Sindh Assembly.
The former minister said that WAPDA sources disclosed that project colony and model village at Bhaha dam is under construction however actual project is yet to start.
History shows that some political parties with the alleged support of India have opposed the construction of Kalabagh Dam. Some politicians and feudal lot are said to have been on the Indian pay list just to oppose the dam.