day, we saw hundreds of migrants at this temporary processing site, waiting in line to load on to buses, many of them children, at least 18,000 unaccompanied minors crossed in july. >> when you have kids, family units crossing in very remote areas in 100-degree heat, that is problematic. >> reporter: that's the case in mcallen, texas, where a declaration of emergency was ordered by mayor javier villalobos. why have you guys had to step in here? >> because if we don't step in, then we have 1800 immigrants dropped off here in mcallen wandering around. >> reporter: villalobos tells us he's also facing a health crisis. the number of migrants testing positive for covid has been trending up, 7,000 since february, but 1,500 just this past week. most will quarantine in this park that's now being used as a temporary shelter run by catholic charities. >> we have no authority to stop