NY400: Holland on the Hudson was the 2009 commemoration of the 400th anniversary of Henry Hudson's 1609 expedition up the river bearing his name, that later provided the basis for the founding of New Netherland. The 2009 commemoration was inspired by a Dutch-American Foundation, Henry Hudson 400, that organized a chain of events in the Netherlands and New York during 2009. The peak of activity in New York City was NY400 Week, September 8-13. It was also the occasion for environmental thinking, including the Mannahatta Project reconstructing the ecology of 1609 Manhattan.