A civil engineering group that surveyed Indiana's infrastructure has given the state's dams and wastewater treatment systems low marks and says roads, bridges, dams, railroads, airports and treatment plants need billions in improvements to meet future needs.

The report by the Indiana section of the American Society of Civil Engineers gave Indiana a D+ in its first report card on the state's infrastructure. That's slightly better than the D grade given nationally.

The report rated each type of infrastructure on a seven-component scale by engineers who specialize in that category. Grades were based on condition, capacity, operation and maintenance costs, future funding and public need.

Bridges fared the best, earning a C+. The state's lowest grade was a D- for both wastewater treatment and dam conditions. Airports received a C, roads a C- and rail and drinking water were both rated D+.

"While some improvements have been made over the past few years, much work remains," engineer Katherine Graham, who supervised the report, told The Times in Munster.

The report did not suggest how to pay for improvements as Indiana's struggles with dwindling tax revenue and a disappearing surplus despite millions in cuts.

Indiana Department of Transportation spokesman Will Wingfield said funding for roads and bridges depends heavily on spending decisions at the federal level.

He said the state also is using money from a lease of the Indiana Toll Road to develop projects that encourage new business and residential development.

"Our long-term goal is to use this infrastructure that's being built to spur jobs in the private sector and growth in the private sector," Wingfield said. "That is what's going to really help everyone else along."

Karl Zimmerman, an assistant professor of engineering at Valparaiso University, said Indiana should focus on maintenance for current systems, especially water and wastewater systems whose failure can affect human health.

"We have a tendency here in the U.S. to buy new and throw away when done. Infrastructure doesn't work that way," Zimmerman said. "We have to maintain it, because it's way too expensive to keep buying new.