Antibiotics in the world's rivers have reached dangerous levels, according to a new study led by researchers from the University of York. Antiobiotic pollution encourages bacteria to develop resistance to certain 'life-saving' medicines, making them ineffective. Last month, the UN declared antibiotic-resistant bacteria, a global health emergency. Some of the most famous rivers across the world including the Thames are contaminated. Waste dumped into the rivers and sewage are the leading causes.