Earthen barriers have been set up across a creek and water was being tested Thursday around the site of a nearly three-million-gallon leak of saltwater generated by oil drilling, the largest spill of its kind in North Dakota’s current oil rush. The berms were built at Blacktail Creek to prevent potentially contaminated water from flowing out of the creek and into a bigger body of water that leads into the Missouri River. The pipeline operator, Summit Midstream Partners, and state inspectors will keep testing the soil and water at Blacktail Creek and the larger Little Muddy Creek. The saltwater produced by oil and natural gas production is much saltier than seawater and may also contain petroleum and residue from hydraulic fracturing. The spill was detected Jan. 6 during a periodic inspection by the company, which said Thursday that the cause of the rupture in the pipeline and when exactly it happened were still unknown.