And they're Beavers. 14 Eurasian beavers arrived in Ulaanbaatar from Bavaria, Germany this week.
Known as ecosystem engineers, the hard-working beavers build dams that have positive effects on the ecology. According to Wikipedia:

Beaver ponds, and the wetlands that succeed them, remove sediments and pollutants from waterways, including total suspended solids, total nitrogen, phosphates, carbon and silicates. Source

Six more beavers will be sent over from Germany later on. According to various news sources, Germany is sending the beavers over for free. 20 more beavers are to be imported from Russia sometime this year. The initiative by mayor G.Munkhbayar is a part of a program to restore the heavily-polluted Tuul river basin, which provides most of the drinking water for Ulaanbaatar city.

The beavers will be bred in a protected environment before being rehabilitated into the wild.
Of course, one questions the logic of pinning our hopes of saving Tuul river on a few families of beavers when there are thousands of human families dumping their household waste into the river. One hopes that this is only a small part of the Tuul river restoration plan.

Beavers are native to Bulgan river, Khovd aimag of western Mongolia. However, according to news reports, Bulgan river beavers have been migrating south to China over the past few years.

If you are curious, below is a BBC documentary segment on how these hard-working animals go about building their lodge.