Randall Clarke Dennis, left, an instructor at the Harbor School, watches students Timothy Morrison, middle, and Lijasad Maxwell, right, as they send 422 oyster reef structures into the Hudson River.

Randall Clarke Dennis, left, an instructor at the Harbor School, watches students Timothy Morrison, middle, and Lijasad Maxwell, right, as they send 422 oyster reef structures into the Hudson River.

Randall Clarke Dennis, left, an instructor at the Harbor School, watches students Timothy Morrison, middle, and Lijasad Maxwell, right, as they send 422 oyster reef structures into the Hudson River.

Randall Clarke Dennis, left, an instructor at the Harbor School, watches students Timothy Morrison, middle, and Lijasad Maxwell, right, as they send 422 oyster reef structures into the Hudson River.