I understand that the best would be for the Jordan to come back, but what's ecologically wrong with this?
Some researchers warn that when large quantitative of red sea waters will pour into the the dead sea the reaction might create plaster like material that would float on the surface. More power and water supply to Jordan means more Arab are going to settle and irrigate the Jordan valley and the Arava, so they will be right on Israel's doorsteps, whereas now the Jordan valley is sparsely populated.
There will be even less water supply to natural streams and the southern Jordan river itself because all these water will be used for human consumption and more waste water will flow into the Jordan river and the dead sea.
Perhaps the worst of all is that by participating in this trilateral agreement the Israeli Judenrats in fact recognize in an international teraty the Palestian claim to the Jordan Valley and most of the dead sea that isn't already occupied by Jordan. It is a very dangerous precedence.