He was also actively interested in art, fishing, nature conservancy, and theater. He was an active supporter of the New York Theatre Guild, where he later served as director overseeing the Guild's operations. He acquired of land along the Carmans River on eastern Long Island for personal use to conserve waterfowl and for hunting. In 1947, Wertheim and his then wife, Cecile, donated the entire stretch of land to the United States government for "the American people"; the land would eventually become known as the Wertheim National Wildlife Refuge.