boundary. (4) Mitigation relief Upon determination that a harmful algal bloom or hypoxia event of significance has occurred under paragraph (2), the appropriate Federal official is authorized to make sums available, from funds appropriated for such purposes, to be used by the affected State, Tribal, or local government, or by the Under Secretary in cooperation with the affected State, local, or Tribal government, for the purposes of mitigating the environmental, economic, social, subsistence, and public health effects of such event. (c) Event of significance policy (1) Publication Not later than six months after the date of the enactment of this section, the appropriate Federal officials shall publish Harmful Algal Bloom and Hypoxia Event of Significance policies for marine and coastal harmful algal bloom or hypoxia events, and for freshwater harmful algal bloom or hypoxia events, respectively. Each such policy shall include the following: (A) Evaluation criteria and considerations to inform the determination of a harmful algal bloom or hypoxia event of significance under subsection (b)(3). (B) The type of supplementary information that an affected State or other eligible requester described in subsection (b)(1) may provide to accompany a harmful algal bloom or hypoxia event of significance request. (C) Process and criteria for prioritizing and evaluating multiple requests for a harmful algal bloom or hypoxia event of significance determination. (2) Opportunity for comment Not later than 120 days before publishing each final policy under paragraph (1), the appropriate Federal officials shall publish a draft of each such proposed policy in the Federal Register for a public comment period of not less than 60 days. (d) Limitations (1) Federal share Except as provided in paragraph (2), the Federal share of the cost of any activity carried out under this subsection may not exceed 75 percent of the total cost of such activity. (2) Waiver The appropriate Federal official may waive the non-Federal share requirements of