Meh, sanity is for the bland anyway. Join us here in the insanity pool, free mimosas every thursday! But in all seriousness, a hawk is a good choice seeing as there are many species out there to pick from. Had you not said that your preference is for small ones i'd have pointed out Ospreys seeing as they're the only ones I know of that frequent aquatic environments. Sparrow Hawks are also an option seeing as they're pretty small, however I can't remember whether or not they're actually hawks, or if it's just a name.