The 10th Circuit upheld a decision preventing the Cherokee Nation from intervening in a lawsuit over watershed pollution from industrial chicken farms...The state of Oklahoma sued Tyson Foods and affiliates in 2005 over alleged pollution from poultry waste into the Illinois River Watershed, encompassing 1 million acres on the border between Oklahoma and Arkansas...[T]he Cherokee Nation...also has an interest in the watershed...The Denver-based 10th Circuit...[pointed] out that the tribe was aware of the litigation for four years, but refused to join until 19 days before trial...Participation as a "friend of the court" should suffice, Judge Harris Hartz wrote...