Northern Portugal

I've asked this before but thought I'd have another go: can anyone tell me
anything about diving in Portugal, not the Algarve but about as far north as
you can go there, up by the Spanish border? I'll be there end July/beginning
Aug. Especially any recommendations re: dive outfits/shops etc. There's one
decent-looking operation in Porto I've found - Mergulhomania - but I was
wondering if there were others, esp. anything further north.

Any info very useful.

Cheers,

Bernard Lyall