I've done the swim at M'man a few times. it's a gravel pit so no currents but there could be chop if it's windy although it's pretty sheltered with waterside shrubbery and banks.
the water will be cold - accept that - but hopefully not as cold as last year when it was sub-11C. I was one of the officials on the day and despite all attempts we couldn't find anywhere where it was above 11C so we had to cancel the swim under BTF rules. most competitors were happy with that as the air temp was only about 7C and it was also pissing down!
in the year's I've done it the water was c14C - cold but tolerable
this year I'm hoping to race on Saturday and officiate on Sunday so should be there again