busy as a beaver

(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
Farlex Dictionary of Idioms.

*busy as a beaver (building a new dam)

 and *busy as a bee; *busy as a one-armed paperhanger; *busy as Grand Central Station; *busy as a cat on a hot tin roof; *busy as a fish peddler in Lent; *busy as a cranberry merchant (at Thanksgiving); *busy as popcorn on a skillet
very busy. (*Also: as ~.) My boss keeps me as busy as a one-armed paperhanger. I don't have time to talk to you. I'm as busy as a beaver. When the tourist season starts, this store is busy as Grand Central Station. Sorry I can't go to lunch with you. I'm as busy as a beaver building a new dam. Prying into other folks' business kept him busy as popcorn on a skillet.
See also: beaver, busy
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

busy as a beaver

Also, busy as a bee. Hardworking, very industrious, as in With all her activities, Sue is always busy as a bee, or Bob's busy as a beaver trying to finish painting before it rains. The comparison to beavers dates from the late 1700s, the variant from the late 1300s. Also see eager beaver; work like a beaver.
See also: beaver, busy
The American Heritage® Dictionary of Idioms by Christine Ammer.
See also:
  • (as) busy as a beaver (building a new dam)
  • beaver
  • building
  • dam
  • 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
As descriptive phrases go, "busy as a beaver" is right on target.