Is this a happy problem?

Beaver boom worries Oslo

The City of Oslo is carefully monitoring its newly swelling population of beavers as the rodents move nearer the capital's sources of drinking water.
Beavers can introduce the parasite Giardia into the water, with diarrhea and vomiting a result, an intestinal ailment known as 'Beaver fever' (Giardiasis) in the USA.

http://www.aftenposten.no/english/local/article1207498.ece

They said "Beaver fever"!