While a cap-and-trade plan for U.S. greenhouse gases is off the table and out of sight in Washington, a market-based plan for cleaning up water pollution in the Chesapeake Bay has emerged as topic A in the sprawling watershed. While details of how a baywide cap-and-trade system for water are murky, debate over it is dividing stakeholders into strange-bedfellow camps and ginning up tensions in the long-running, federal-led restoration effort.