South Stack is one of the major tidal gates around Anglesey.
There is a tidal race on both flood and ebb and the stream runs at 5 knots or more at springs. The pilot warns to time passages for slack water or mantain an offing of 2 miles or more if the winds are fresh. Here at 17.30 of a lovely summer evening, 2 days after neaps, with a light wind of about 5-8 knots and 1 hr 45 mins into the flood the conditions are fine. But don't get lured into a false sense of security, in a blow standing waves 30' high have been reported.