CALAIS, FRANCE   -   A chain of buoys blocks a riv­er in northern France, the lat­est costly measure the au­thorities have deployed in their almost impossible mis­sion to stop Britain-bound mi­grants crossing the Channel. Set up on August 10 near the La Canche estuary, the float­ing barrier is designed to halt so-called “taxi boats” used by people smugglers in re­cent months. The small ves­sels start their perilous jour­neys empty, away from the beaches, before picking up mi­grants from Africa, the Middle East and Asia on the coast. Af­ter 27 people drowned in No­vember 2021 -- the worst ac­cident in the Channel since the narrow strait became a key irregular migration route -- patrols have been stepped up. All along some 130 kilo­metres (81 miles) of coastline between the city of Dunkirk and the Somme Bay, the au­thorities scour the area day and night.The silence of dawn is broken by the purring en­gine of a plane belonging to EU border agency Frontex, equipped with infrared and thermal cameras to rescue stricken migrants alongside drones. Advancing on foot or buggies, an average of 800 se­curity force personnel sur­vey the beaches and dunes ev­ery day. Surveillance cameras have been installed in 12 com­munes and four ports, with the scheme set to be widened in 2024, according to the lo­cal authorities. The cat-and-mouse game between the po­lice and migrants has moved to the coast after security was tightened in 2018 at the port of Calais and the Channel tunnel linking France with southeast England.The area surround­ing Calais now resembles a fortress: fencing and cameras encircle the port and tunnel terminal, while an “anti-in­trusion” wall has been erect­ed beside a road to prevent migrants clambering onto lorries. Fencing also protects parking spots in the Trans­marck logistical zone. “We manage to get in” sometimes, “but it’s difficult”, said Awham, a 23-year-old Sudanese man pushed out of the area by po­lice. As well as battling cross­ing attempts, the authorities are waging a war on places where migrants may gather to avoid the reappearance of camps known as “jungles”.