Bertelsen Nature Park and Stewart Pond are part of the Eugene Parks and Open Space wetlands system - http://tinyurl.com/2jl78a
Following is a quote from Eugene Parks home page:

"The West Eugene Wetlands Program is based upon the West Eugene Wetlands Plan, a multiple-objective, wetlands management and land use plan adopted by the City of Eugene and Lane County in 1992. The Plan was also adopted by the Oregon Department of State Lands and the U.S. Army Corps of Engineers in 1994. It was the first wetland conservation plan of its kind adopted by state and federal agencies in the United States. The City of Eugene's Wetlands Program helps coordinate and implement many elements of the West Eugene Wetlands Plan"