Investigators are working to determine the cause of three separate accidents that occurred along the river on Thursday. The 140-ft. towboat Capt. Russell Simpson ran aground at about 40 miles south of Helena, Ark., at mile marker 626.1. The towboat was pushing 25 barges of dry cargo at the time of the accident. The river wa closed between mile marker 623.1 and 628. The 200-ft. towboat Robert A. Kyle ran aground on Thursday, about 15 miles north of Rosedale, Miss., at mile marker 595.5. The towboat was pushing 32 barges at the time of the grounding. The river was closed between mile marker 595.9 and 594.4 at Victoria Bend. The 128-ft. towboat Noble C. Parsonage ran aground about 180 miles south of Angola, La., at mile marker 265.5.