SIOUX FALLS, S.D. (AP) - The commercial barge season on the Missouri River will be shortened by 47 days because of new water conservation measures in a revised operating manual, the Army Corps of Engineers said.

Runoff above Sioux City, Iowa in June was 56 percent of normal and runoff from mountain snowmelt has been disappointing, said Larry Cieslik, chief of the water management office in the corps' Omaha, Neb., office.

Runoff into six upstream reservoirs this year is forecast to be 15.7 million acre-feet, down from the normal of 25.2 million acre-feet. Water releases from the reservoirs will remain at minimum service levels.

"The navigation season will be shortened 47 days, in accordance with the revised master manual and its more stringent drought conservation measures," Cieslik said.

The commercial navigation season will end between Oct. 6 at Sioux City and Oct. 15 at the river's mouth near St. Louis, the corps said.

South Dakota Gov. Mike Rounds applauded the announcement.

"The latest court decision to allow the Army Corps of Engineers the flexibility to make changes that reflect the need to conserve water and protect the rights of upstream states is a change over the old system," Rounds said in a statement.

"We are pleased the corps is responding positively to the changes in the master manual. We simply don't have the water in the upper basin to flush downstream for a few barges."

The level of the three northernmost reservoirs will fall even more in July, the corps said.

Lake Oahe will end the month 33 feet below average, Lake Sakakawea will end the month 28 feet below average, and Fort Peck will drop to 35 feet below average.