Has either of you been to the barge wrecks in the middle of the river? From memory you have to drop in from a scout hall on the southern bank of the river and surface swim about 50~100m to a marker buoy. It's a night dive because of the river traffic but had a huge amount of marine life on the wreck. There's also (or at least was) a line that someone had run to what remains of a what was supposedly a chinese junk.

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Air is for pussies.