Upvote:3
Cold water is all relative, where I live anything above 16C is considered warm, under 12C is considered cold :)
North western shore of Portugal (Viana do Castelo) is about 16C - 19C (60F - 66F) South eastern shore of Portugal (Tavira) is about 20C - 24C (69F - 74F)
Algarve region of Portugal definitely seems to be the best part to do snorkeling, especially if you are not used to big waves and currents. But as always the best thing is to do some research on the internet on various areas and then contact a few tourist/scuba places in and around the area you are thinking of traveling too to see what is on offer. Might even be a good idea to go with these schools to learn the safe spots.
As for fishing that would depend on what kind of fishing you wish to do, but looking at this site there is definitely scope for some fishing: Fishing Portugal
Some temperatures can be seen here: