Dams and barrages upstream river Indus have put paid to much of Indus delta's biodiversity. Undivided Punjab's irrigation system was established in the 1890s. In 1932, the Sukkur barrage was built reducing freshwater to the Indus delta. In 1958, the Ghulam Mohammad barrage became operative and in the early 1960s, the world's largest earth dam, Tarbela dam, was built on the Indus.