The Diablo 2 Wiki
The Diablo 2 Wiki archive is available for anyone looking for information on Diablo 2. All information here is pre-D2R but contains a lot of useful information that is still relevant. Updated sections for new D2R features can be found on the PureDiablo Diablo 2 section

Frozen river

From Diablo 2 Wiki

Frozen River is found in the Crystalline Passage. And it is the place you are looking for if you are doing the Anya quest.