Nobody is sure why the water level on the Ganges receded at Farakka, where India built a barrage in the 1970s to divert water away from Bangladesh. Much later, in the mid-1990s, the countries signed a 30-year agreement to share water. (The precipitous decline in water levels happened during a 10-day cycle when India is bound by the pact to divert most of the water to Bangladesh. The fall in level left India with much less water than usual.)

That will end well.