Boulders and other large rocks are blocking repair crews’ access to the collapsed sewer pipeline that allowed millions of gallons of wastewater to spill into the Potomac River in January.

There has since been a “minimal amount” of wastewater entering the river, including from problems with water-pumping equipment and snowmelt carrying sewage from a nearby creek into the river, said Sherri Lewis, a spokesperson for DC Water, the public utility that oversees the pipe.

The utility company said in a press release that its crews will need up to six weeks to divert more wastewater and prepare the Potomac Interceptor system for heavy machinery to remove the rocks.

A DC Water video inspection revealed that rocks are obstructing the pipeline 30 feet downstream of the collapse.

A makeshift piping system is diverting wastewater from the broken section and is containing most of it, DC Water said. But crews must reach the collapsed section to determine why it broke and to repair it.

The collapse occurred at a part of the sewer line that runs along the Clara Barton Parkway in Montgomery County, near the Potomac River and the Chesapeake & Ohio Canal National Historical Park.

The large rocks clogging the pipeline lay on top of it before the collapse, according to DC Water, which provides water and wastewater treatment to Washington and wastewater treatment for 1.8 million people in Maryland and Virginia suburbs.

Construction crews likely excavated the rocks to build the pipeline in the 1960s and placed them on top as backfill, according to DC Water.

When the pipeline broke in January, the rocks collapsed onto it and the flowing wastewater forced the rocks downstream, where they created a dam, the agency said.

Rocks and soil that previously surrounded the pipeline have also entered it, further obstructing it.

A local environmental group, the Potomac Riverkeeper Network, has said the collapse caused catastrophic levels of wastewater to spill into the Potomac.

Two weeks ago, the group reported that E. coli levels near the pipeline collapse were thousands of times above the acceptable level for human contact.

Levels of the bacteria have mostly descended in recent days, according to DC Water, but they remained elevated and unsafe near unhabited Swainson Island, near the Cabin John community.