[Lindsey]
Uniting against a common enemy also prevents the hassle of fighting a three-way battle.
My days of world-saving are over, but I offer a suggestion. Tell him to freeze the contaminated bays and estuaries; focusing on where they lead into the defunct sanitation plants. It's a temporary measure, the water being as warm as it is here, but if done correctly, it could buy you several days and keep the contamination from spreading further inland or offshore. It will also choke the plants and keep more water from being consumed within the city.