Some beaver folk for all your river damming needs. In an open world like my Haven campaign, I find it problems with a river to be an excellent way to incentivize players to expand the map.
https://mindweaverpg.wordpress.com/2021/06/01/biweekly-monster-castorid-add/
The party ended up getting a little sidetracked by a whole nest of ogres.
#playreport
https://mindweaverpg.wordpress.com/2023/06/30/play-report-kotb-barrier-march-session-52-surprise-ogres/
Searching for more information about the lay of the land around the bugbear crag, the party ends up ambushing a patrol, but when the ambush doesn't get surprise, the battle is far more even than intended.