Why it took 40 years for Hilsa to swim up to Allahabad again

After over 40 years, hilsa will be able to swim down the Ganga up to Allahabad. The migration of Hilsa till Allahabad had been possible till a barrage was built across the Ganges at Farakka in Bengal in the 70s. The barrage came with a navigation lock that blocked its movement. This lock has now been redesigned to ensure safe migration of hilsa shoal.

from Times of India http://bit.ly/2WN6Awp
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