Drowned hopes - Donald E. Westlake

Dortmunder's past comes back to haunt him when he returns home after an unsuccessful burglary and finds his old cellmate sitting in his living room. He needs Dortmunder's help in retrieving $700,000 that he'd buried in a small town 30 years before. The problem is that, while he sat in jail, the State of New York flooded the area to build a reservoir; the loot is now under a few feet of dirt and many feet of water. Being a man of great determination but few ethical principles, the thief plans to blow up the dam, emptying the reservoir but also flooding the inhabited countryside to get at his stash. Dortmunder pleads with him to be allowed to retrieve the money another way. His first attempt fails. And his second. And third. Meanwhile the thief is losing patience...