This particular issue is discussed here by Atle Hindar, NIVA - a scientist with years of experience within this field and perhaps the most knowledgeable of experts in Norway:
Acidification is one of many threats to the valuable Atlantic salmon species and has wiped out salmon populations from many Norwegian rivers during the last decades. Due to reduced emissions of sulphur dioxide in Europe relative to 1980 and especially due to an extensive liming programme, many rivers now support viable fish populations again.
