whn - incoming tide {2 of 2}

There is an 8.3m high [spring] tide outside the sea lock, and a certain amount of seawater is allowed to overflow the gates - although the marina is already quite full with the rusty water.
"Cracking" the outer gates open by a small amount at high tide is part of the usual process needed to "flush" the marina. Sadly the present pollution by mine waste water is largely preventing that.