The Trump administration has delayed indefinitely a plan for strengthening defenses on a crucial Chicago-area waterway to prevent Asian carp from reaching the Great Lakes, where scientists say they could cause severe harm to native fish populations, officials said Tuesday. The US Army Corps of Engineers had been scheduled to release draft results of a study begun in April 2015 on possible structural or technological upgrades at the Brandon Road Lock and Dam near Joliet, Illinois, a few miles downstream of a network of electrical barriers intended to repel the carp.