From the FAA website:
"While waterbombing from an altitude of 17,999 ft has proven totally ineffectual, studies have shown that the reduction in carbon emissions and noise pollution totally validates the unnecessary shutdown of large blocks of airspace to general aviation. Therefore all future airborne firefighting will be performed at 17,999 ft. for months at a time, regardless of actual fire containment."
(Disclaimer: the preceeding was 100% void of non-fiction)