Thanks Phillbo. I asked the same neighbour who told me about the electrical leaks if he swam in the marina to check things. My plan was to go tug on random things to see if anything was loose that shouldn't be loose.
His response was "Sure! I've got a mask right here if you want to borrow it. But... make sure you wash yourself off with the hose after - there are things in there..."
Electricity notwithstanding, I'm no longer terribly eager to go in the water.