You yourself wrote in this thread:

> There’s fish eggs being washed everywhere during rain storms. The eggs come from upstream and wash into random places.

Do you realize that in the summer mountains below 4000m are mostly snow-free and thawing point ie in Europe has been pushed above 5000m repeatedly during summers. Its easy to have 25C in 2500m in today's alps (ie today 22C in 2000m in Chamonix, France).

The term 'alpine lake' doesn't mean anything specific, and most are fed from rain during entire summer without any/much of snow or ice contribution.