Over a thousand large dams in India will be roughly 50 years old in 2025 and such aging structures across the world pose a growing threat, according to a UN report which notes that by 2050, most people on Earth will live downstream of tens of thousands of dams built in the 20th century. The report, titled 'Ageing water infrastructure: An emerging global risk' and compiled by United Nations University's Canadian-based Institute for Water, Environment and Health, says most of the 58,700 large dams worldwide were constructed between 1930 and 1970 with a design life of 50 to 100 years.