Beavers, Dams and lodges.

Beavers are amazing semi aquatic Key Stone species that deserve representation in Minecraft. 

 For starters, I think there could be a random structure that’s possible to find in two forms- lodges (located in a lake or pond) and damns (located in rivers). These areas may also have increase odds of spawning fish to reflect the role beavers have in establishing ecosystems. These structures can consist of wood logs (varying on the trees around the structure) and perhaps using the upcoming mud blocks. There could also be a 1x1 underwater entrance into a very small interior where the beavers will live.

 Beyond the structures itself, the beavers themselves would probably be about the size of a Minecraft wolf. The beavers will roam around the structures and swim. If a mob approaches too suddenly, the beaver may attack or use its tail to slap the water to threaten something moving too close and too fast. Beavers can be breed using potatoes or carrots and while adult beavers cannot be tamed, baby beavers can be and will not attack the player who breed them, as beavers can imprint on humans. Beavers could also strip the lowest block on trees that they come in contact with, also dropping sticks in the process (they can also pick up sticks). I also think it could be cute if they had an animation of sitting and eating snacks and perhaps one of them cleaning themselves.

 I think beavers would make a fine early game addition to help make Minecraft a more vibrant and informative experience.