Recently, the True Nature Foundation has announced that Carpathian water buffaloes have been released in the Danube delta of the Odessa region, Ukraine.
See here, here and here.
I already mentioned the water buffalo project of the TNF in a 2015 article. Back then, it was the intention to crossbreed domestic, locally adapted water buffalo with wild Asiatic water buffalo to achieve a mix of locally adapted and wild type traits. Seemingly this idea has been rejected, perhaps for practical reasons, since the project has announced that the recently released herd is composed of Carpathian water buffalos. Therefore they are domestic descendants of the wild Asiatic buffalo, Bubalus arnee. This species is not native in the area, but Europe once was home to Bubalus murrensis, the European water buffalo. So when domestic water buffaloes are released in Europe, it based on the assumption that both species are ecologically similar and that domestic water buffaloes can fulfill a niche that has been left vacant when the European water buffalo disappeared (for anthropogenic reasons or not). And indeed water buffaloes do have a positive effect on biodiversity in reserves of a certain type (for more details, see the 2015 article and literature cited). However, there is no evidence for Bubalus on the area of the former USSR except for one possible horn element from the Taman island, Russia .
Nevertheless, I do think that water buffaloes can have a positive effect on biodiversity in the Danube delta of the Ukraine. I assume that studies will be conducted documenting the effect of this megaherbivore species being introduced in this area.
 Diana Pushkina: The pleistocene easternmost distribution in Eurasia of the species associated with the Eemian Palaeoloxodon antiquus assemblage. Mammal Review 37 (3), 2007