Who can say that snorkeled in Alaska? It was a unique and amazing experience. The guides are very knowledgeable. The group is small so everyone can have the chance to explore a lot without it being too crowded.
Yes, it is cold but, as they say, the biggest issue will be getting in and out of the very thick wet suit. It was a funny experience, me and my friend couldn't stop laughing at each other.
Just do it! It's totally worth it!