Spanish fishermen protested against the creation of an artificial reef in the bay of Gibraltar on Sunday and claimed the territory's authorities were blocking their access to the waters in the latest focus of tensions between Spain and Britain.
For just over an hour some 30 fishing boats circled where 70 three-ton concrete blocks were dropped in July to form a reef that Spain said was not legal and prompted the government to ramp up border checks with the British overseas territory.
The extra controls, which have caused long waits for the thousands of tourists and locals, led British Prime Minister David Cameron to call on the European Commission to urgently send a team of monitors.
Britain claims the measures are “politically motivated and disproportionate,” while Spain says it will sue Gibraltarian authorities for environmental damage from the reef.
In retaliation, Spain has threatened to impose a 50 euro (67 US dollar) border fee on tourists, restrict air space or block the enclave's lucrative ship fuelling business.
Meanwhile, the fisherman claim that the dispute over the shared waters around Gibraltar has cost them 1.5 million euros in potential income over the last year.
The territory has a population of 30,000 and relies on tourism, online gaming and offshore banking, and was ceded to Britain by Spain in the 1713 Treaty of Utrecht.