To quote from Wikipedia, "The park provides an excellent resource for environmental studies, wildlife observing, fishing, and other recreational activities made possible by easy access to the Potomac River. Fourteen buildings and two structures are located in the historic district and associated with the property's sequential development as a plantation, an institutional agricultural complex, and a farm museum."
Of the park's 512 acres, 289 are included in Oxon Hill Farm, which is on the National Register of Historic Places. Taking 300 acres, over half the park, would plainly entail taking over 75 acres from the farm, about a quarter of its area. The subsequent development, besides being an eyesore for the remainder of the farm, would destroy wildlife habitat and many plants beneficial to the environment, while creating a vast paved surface near the river which would produce harmful storm water runoff into the bay.
It is a pity the governor has no respect for history, the environment, or the people who currently enjoy the quality of the park. It is to be hoped the legislature has enough sense to block this foolishly destructive proposal.