DUBUQUE, Iowa (AP) — Work on Mississippi River locks has caused a sudden drop in river levels in Iowa, surprising marinas and leaving some boats high and dry. The Telegraph Herald reports that crews at Lock and Dam No. 10 in Guttenberg closed the dam’s gates Tuesday, decreasing the flow of the river. Scott Pettis is the hydrologic technician for the U.S. Army Corps of Engineers’ Rock Island District. He says the water level at the Dubuque railroad bridge had dropped about 1.5 feet (0.46 meters) by Wednesday.

Pettis says dips in the river level are normal when water flow is lower, but such a steep drop is unusual. Nathaniel Anderson is a civil engineer for the Corps’ St. Paul District. He says the drop started in Wisconsin on Sunday.