Where to Find and Catch Whiscash
From Pokemon Go Wiki
Whiscash are found and captured in Nest and Habitat locations.
Nests
Whiscash Nests are locations that consistently spawn Whiscash.
Habitats
Whiscash Habitats are spawn locations where Whiscash is likely to be encountered, but not guaranteed the way a Nest is.
Additional Tips and Information
Best Nests
If you know a really good nest or any of the nests above is really good, list them here: