London - Environment experts may have to restock a stretch of river after the recent hot weather killed 20,000 fish, it was disclosed yesterday. The fish suffocated after oxygen levels plummeted in the waters along a 2 km stretch of the Old Bedford River at Sutton Gault, Cambridgeshire. Experts from the Environment Agency were called to the river, where they found thousands of dead roach and perch, and several hundred dead pike, bream and tench.