A couple of weeks ago I was pottering along off Clacton with somewhere in the region of 25 other vessels of varying size. headingwest on an incoming tide which does run a bit quick at times, I saw the yacht infront of me (about 50yards) suddenly vear to starboard towards the shore which was about a quarter of a mile, he could not go to port because on closer inspection there was a drift net set up in a semi circle about 10 yds to his port side with no flag marks or anything all you could see was the occasional float on the top line. I was motoring at the time - so hard astern and tea all over the cabin sole.
I agree they should be well marked and not in a "normal channel" for vessels from the Colne