Derry businessman and European election candidate, Peter Casey, has planted a tricolour on Lough Foyle to "reclaim it for Ireland".
Mr. Casey, who is running as an Independent in the Midlands-North-West constituency next week, hoisted the flag outside his home in Greencastle, in protest at Britain's strongly disputed claim to the waters and seabed of the Foyle - both lough and river - up to the high water mark on the Donegal side right up to the town of Lifford.
The former Dragons' Den star released a video of himself raising the colours and stating: “I’ve just reclaimed Lough Foyle for Ireland."
He said: “The Crown claims ownership of the water just outside my front door and right out to the end of Lough Foyle. Ireland, quite rightly, lays claim to its half of the waterway. However that will have major implications for shipping bound for Derry port, as the channel is on the Donegal side of the lough.
“It’s somewhat akin to the Rockall ownership dispute, but a lot closer to home."
London's claim to the Lough, based on a 17th Century Royal Charter that established the County of Londonderry, has been consistently disputed by Dublin, and has had implications for aquaculture in the contested waterway over the years.
Mr. Casey said: “I don’t accept British claims that all of Lough Foyle comes under UK jurisdiction. I’ve raised our flag here simply to highlight the issue in the hope that an amicable and fair resolution can be reached between Ireland and the UK.
"If Britain does finally leave the EU, then it will be operating under different fishing rules, so this really is an area where agreement is needed."
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