Sure, you can seize the damn, but if you cut off the water, the entire population suffers. ISIS, who still has the cities and ears of the people and farmers, blames you. Farmers listen to the propaganda and now hate you. You're now worse off than when you started because now people expect ISIS to retaliate and the farmers are inclined to help them because they want their water back.
ISIS has been somewhat successful in holding ground because they seem to be providing some sort shaky of infrastructure to the people. My question is on how to cutoff ISIS' ability to provide that infrastructure without generating the ill will of the people because now they have to suffer. Essentially, I believe the only answer would be covert sabotage, such as rendering the dam ineffective but not destroying it, combined with solid information operations to blame it on ISIS' incompetency. Although the people have to suffer due to lack of infrastructure, ISIS takes the heat, not you.
Anyone that wants to chime in, please do. I'm just trying to generate ideas on effectively defeating ISIS other than the "kill em all" approach.
ISIS, doesn't control the dam, the Iraqi forces have already secured it. ISIS does however, control a few oil wells, and those should be secured IMO. Geographically its a bit difficult without deploying large amounts of forces on the ground, with follow on support and opening up lines of communication (I.e. secure traveling routes for resupply and transport of oil). It would take a lot of troops and would cost alot of lives and equipment.
ISIS, is not necessarily providing an infrastructure to local populations, they are bringing a government structure that is inline with that areas tribal and religious belief's.
The only way to make ISIS look as the bad option would be to make those areas somewhat autonyms government regions or allow them to break away from Iraq/Syrian governments and form their own government and or state. Iraq and Syria will most likely not do this, due to the oil rich areas and nationality. It would be like Texas saying we no longer want to be part of the US, so we're breaking away and keeping all our oil, just ain't gonna fly.
Going forward, those area's as Freefalling alluded to, will have to become tired of ISIS and seek outside help in overthrowing and removing ISIS (Your classic SF mission).
The kill them all, or at least kill them there instead of here strategy, is a counterterrorism strategy. No, we cannot kill every single ISIS fighter, but we can kill as much of them as possible, and make it undesirable to join and or continue fighting for ISIS. Keep them busy there vs giving them time and space to plan and attack here.
Another option is a scorched earth, where we just destroy everything and everyone (this will probably be the Russian strategy) and although it will work in many aspects, the residuals effect's will be a follow on generation that will have a deep burning hate for the west/russia and the cycle will continue down the road.
The last option is genocide, kill their children's, children's, children. Remove that particular sect of Islam from humanity permanently. I imagine at some point the world as a whole will have to come to terms with this and accept it, if we want to move forward and out of the Islamic Terrorism age.
So no there really are no good options or golden bb options in dealing with this problem. If there was, we would've done it long ago.