Blockage of natural flow of domestic waste water by the nearby landlord

Ours is a rural area. Just beside our house there's a drainage canal . Earlier it used to flow in south to north naturally . But 15 years ago 2 neighbours who are staying at the back side of our house has blocked the way and made it in a way that the drain water started to move in north to south direction. We didn't raise any issue as the water is flowing without being stagnant. There is a house in front of ours and backside if it is of completely open fields which are being used for agriculture since ages. Recently the tenant of the Agricultural plot which is just beside the drainage canal has blockaded the flow of drainage water by stating that the drain water is entering the fields. (Its not even overflowing though) but we argued him by saying that " it's been in that way since 15 years . No one had raised any issue with it . It's not even hampering the Agricultural work". But the owner called and threatened us by stating that he will fully block the path by taking advantage of the political power. So respected sir, can you please tell me what laws supports this case and how to deal it in a legal way if it requires. Thank you so much.