Upon a determination under paragraph (2) that there is an event of national significance, the appropriate Federal official is authorized to make sums available to the affected State or local government for the purposes of assessing and mitigating the detrimental environmental, economic, subsistence use, and public health effects of the event of national significance.

The Federal share of the cost of any activity carried out under this paragraph for the purposes described in subparagraph (A) may not exceed 50 percent of the cost of that activity.

Notwithstanding any other provision of law, an appropriate Federal official may accept donations of funds, services, facilities, materials, or equipment that the appropriate Federal official considers necessary for the purposes described in subparagraph (A). Any funds donated to an appropriate Federal official under this paragraph may be expended without further appropriation and without fiscal year limitation.

At the discretion of an appropriate Federal official, or at the request of the Governor of an affected State, an appropriate Federal official shall determine whether a hypoxia or harmful algal bloom event is an event of national significance.

In making a determination under subparagraph (A), the appropriate Federal official shall consider the toxicity of the harmful algal bloom, the severity of the hypoxia, its potential to spread, the economic impact, the relative size in relation to the past 5 occurrences of harmful algal blooms or hypoxia events that occur on a recurrent or annual basis, and the geographic scope, including the potential to affect several municipalities, to affect more than 1 State, or to cross an international boundary.

The term “event of national significance” means a hypoxia or harmful algal bloom event that has had or will likely have a significant detrimental environmental, economic, subsistence use, or public health impact on an affected State.

The term “hypoxia or harmful algal bloom event” means the occurrence of hypoxia or a harmful algal bloom as a result of a natural, anthropogenic, or undetermined cause.