PERIPRAVA, Romania, Oct 17 (Reuters) - A big Ukrainian dredging barge noisily churns mud from the bottom of the Danube river under the watchful eye of armed Romanian frontier guards on patrol boats stationed nearby. The European Union, Washington and environmentalists have slammed Ukraine's work on a 165-km (100-mile) shipping canal in the sensitive Danube delta and the project has also ignited a potentially explosive border stand-off.