STILLWATER -- The St. Croix River Bridge has fallen a year behind schedule due to problems attributed to its complex design.

The mile-long bridge to connect Minnesota and Wisconsin involves an estimated 42.3 million pounds of steel and 564 million pounds of concrete.

It will replace the 85-year-old Stillwater bridge 2 miles upstream. The span of the river where the new bridge is being built is known as Lake St. Croix.

The bridge design resembles a jigsaw puzzle - a complex design that to Minnesota Department of Transportation manager Michael Beer said is the reason for the delayed schedule.

It isn't yet clear whether the delay will cost taxpayers or the general contractor more. MnDOT and the Wisconsin Department of Transportation budgeted $30 million in contingency funds.