A settlement that ends court challenges to deepening the Port of Savannah’s busy shipping channel could still fall apart if a federal agency doesn’t prove machines are capable of artificially boosting oxygen in the water to help fish breathe. The agreement last week in U.S. District Court allows the federal government to move forward with a $652 million plan to dredge more than 30 miles of the Savannah River between the port and the Atlantic Ocean to make room for the supersized cargo ships that will be used when the Panama Canal is deepened. Deeping the harbor is expected to boost all of the state’s industries, especially agriculture.