(also Iaso’da), a river in Brest Oblast, Byelorussian SSR; a left tributary of the Pripiat’ of the Dnieper basin.

The Iasel’da is 242 km long; the area of its basin up to the place where the Pina River joins the Pripiat’ is 5,430 km. The river rises east of the Belovezh Virgin Forest and passes through Lake Sporovskoe. It is fed by various sources, but predominantly by snow. High water occurs from March through May. The mean flow rate 53 km from the mouth is 16 cu m per sec. The river freezes over in November or December, and the ice breaks up in the second half of March or the first half of April.

The Iasel’da is connected with the Shchara River of the Neman basin by the Oginskii Canal; through the Pina River it is connected with the Mukhavets River of the Bug basin by means of the Dnieper-Bug Canal. The Iasel’da and its tributaries are canalized in places. The city of Bereza is situated on the Iasel’da.