Forget what the AT says Bob, its not at all straightforward, particularly marinas. There is no single simple answer. Some waters with direct connections to rivers are regarded as 'stillwaters' some are not. I think a lot of it is down to historical precedent and whether your local EA chap got out of bed on the right side that morning. I am not joking, it's as haphazard as that.
I went through this nonsense last year and had something of a result on my local marina where the EA made a decision that part of the marina was in and part of the marina was out. Crazy, but I was grateful. Marinas are a particular problem since whether the EA is on your side or not, the final word is with the marina management. My marina is happy to accommodate anglers so long as there is no nuisance to other marina users and you MUST have a boat moored permanently in the marina from which you must fish.You can't just casually stroll in or motor in and start fishing, wherein lies another problem. Marinas are private places and for security reasons don't usually accept casual fishermen. Shepperton Marina connected to the Thames has a 'no fishing under any circumstances' rule even if you are a boat owner, however connected to the marina are the RMC pits where it's fishing business as usual. There is a complete lack of clarity or guidelines as to the legal position of any so-called private water which is accessible from the river. The owners of the properties tend by and large, to discourage casual boat visitors, but someone in the British Waterways hierachy once told me that technically they cant stop you going into the marina in your boat and fishing (assuming no close season of course)if you don't touch the sides or bottom ie don't moor up to the jetty or don't plant an anchor. Whether thats true or not nobody seems to know.
I think this whole issue is kept fluid by the authorities so they can make pretty much any decision they like about any given set of circumstances. Yet another good reason to dump the close season.