Not sure that Scottish fishing ports as I knew 40 years ago exist now but recent visits to Port Patrick , Kirkcudbright , Nairn , Arbroath and St Andrews show nothing like the pollution I mentioned although I agree that close to Edinburgh I would not eat the mussels
I assume the marina was built using EEC money . That being so the local authority must have had some input in the financing and planning of the infrastructure and there must have been EEC conditions stipulated . The fill site sticks up like a large cliff as you go past in the canal and you can definitely smell it . Who in their right mind would place a land fill site close to an enclosed wetlands and tourist area and allow all the effluent to seep into the system with PCB's and all the accumulated stuff that people throw into their rubbish bins not to mention toilet paper and the threat of typhoid (viz recent case of para typhoid reported in a yachting circle ).
There are fish farms in the area and that junk must be getting into the food chain
Entering the water in the marina was definitely a no no without a full face mask and rubber suit and while I have witnessed careless spills in the past what I saw was reckless - perhaps enormous was an overstatement but I got the impression from the fumes that if I dropped a match the whole thing would have gone up . There was no supervision and the fuel smell was bad . this was not the only occasion
Remember first impressions are pretty close to the truth . I must not be the only one to notice . This was off season too