Boats pulling into Yorkshire harbours could soon be asked to put dye tablets in their toilets as a way of stopping them emptying waste into the water.
From this month, vessels are banned from emptying their toilets and waste water in harbours in Scarborough, Whitby and Filey Coble Landing.
Scarborough Borough Council said the move is to improve water quality.
It said the tablets release a non-harmful dye which will help identify which boats are polluting the waters.
Guidelines on the council website state: "Vessels may be asked to place a 'disclosure' tablet into their toilets or holding tanks.
"It is believed that our Yorkshire harbours will be the first in the United Kingdom to use this innovative approach to identify polluters and these measures have been welcomed by the harbour community and the Yorkshire Bathing Water Partnership."
Rather than empty waste water into the sea, boat owners can pump it into a facility at Whitby Harbour and there are also disposal points for for chemical toilet waste.
The council said holding tanks may only be emptied into the sea more than three miles offshore so waste is not carried back towards the coast and beaches.