Anne Arundel County imposed an indefinite development moratorium in parts of the county after its sewage system hit a limit for maximum volume in wet weather, the county’s Department of Public Works said Monday.

The unusual order, announced late Monday, means that no new construction can occur across much of northwest Anne Arundel County, including Arundel Mills and the BWI Business District — a building prohibition that could last for years. The area encompasses parts of Hanover, Linthicum Heights and Pumphrey, according to a published notice.

County officials initially included Baltimore-Washington International Thurgood Marshall Airport in a map of the moratorium area, but have since said BWI is not affected because it connects directly to Baltimore City.

In response to questions Tuesday, an Anne Arundel County spokesperson did not specify causes of the bottleneck but called the decision a proactive measure to manage the regional wastewater system and prevent sewage overflows. While flows are currently within acceptable levels, county officials said weather conditions have at points pushed the system over its limits.

The sewers in northwestern Anne Arundel County connect to a sprawling system overseen by an agreement between the Baltimore City and Baltimore County public works departments, serving around 1.6 million people across the region. Both the city and Baltimore County have operated under court-enforced federal consent decrees for more than two decades to stem sewage overflows across the system.

Because of the consent decrees, there isn’t additional capacity for this area, which Anne Arundel Public Works officials said has created an “immediate bottleneck for new development.”

“Our multi-county team exhausted all options before arriving at the conclusion that we cannot approve any new connections in these specific areas,” Anne Arundel Public Works Director Karen Henry said in a statement Monday. “Our primary focus is to protect the health of our residents and the environment by avoiding sanitary sewer overflows.”

Amy Mininger, a spokesperson for Anne Arundel Public Works, said Tuesday that county officials learned in early February from Baltimore City that they could not purchase additional capacity in the sewage system, prompting the suspension that the county described in its news release as an “emergency.”

Mininger said the county is aware of 18 developments potentially impacted by the moratorium, though she did not specify how many housing units these projects would create.

Anne Arundel County plans to honor permits for projects that already have been approved for hookups to the sewage system, but projects that hadn’t secured these approvals prior to Monday’s notice are on an indefinite hold, public works officials said.

According to details shared by Anne Arundel Public Works, constraints within the sewage system are tied to Baltimore County’s Patapsco Pumping Station and a sewage pipe known as the Patapsco Interceptor, which follows the Patapsco River along the border between Anne Arundel and Baltimore counties, not far from South Baltimore’s Patapsco Wastewater Treatment Plant.

Mininger said Anne Arundel officials are working on a plan that could divert sewage to other wastewater treatment facilities in the Patuxent or Cox Creek areas.

Construction of such a diversion would take up to five years, Mininger said.

Baltimore City Department of Public Works spokesperson Mary Stewart said the city is not responsible for local development decisions, only treating and discharging wastewater and providing other jurisdictions with modeling on its system’s capacity.

While Anne Arundel County officials said Baltimore made them aware of capacity constraints last month, Stewart said Baltimore City learned of plans for the development moratorium on Jan. 23. City public works officials are not aware of constraints contributing to development restrictions anywhere else in the system, she said.

A Baltimore County spokesperson did not immediately answer questions.

Anne Arundel County Councilman Pete Smith, who represents the impacted area in his county, said he knew nothing about sewage capacity concerns until seeing Monday’s notice. The overwhelming majority of Smith’s district falls under the moratorium area, which he described as an “economic engine” for the region. He expressed frustration he wasn’t alerted to an issue sooner.

“I am flabbergasted,” Smith said. “It’s crazy that we find ourselves in this situation.”

The councilman had yet to talk with public works officials or County Executive Steuart Pittman but said he had many questions about how the area got to this point and why funding wasn’t allocated sooner to avoid it.

Matt Minahan, chair of the Growth Action Network in Anne Arundel County, said this moratorium came “out of the blue.”

Minahan said he was aware of one prior sewer moratorium like this in Anne Arundel County, on the Mayo Peninsula in 2008.

“The history of these kinds of things is they take a couple of years to get resolved,” he said. “There can be a backlog of applications, and once the moratorium is lifted, there is a big flood of development activity.”

In a statement, Pittman said he appreciates residents’ patience.

“We all want to lift the moratorium on new allocations as quickly as possible,” he said, “but we must put the wellbeing of our residents first.”

Though the bottleneck has occurred at a nexus of several jurisdictions — Anne Arundel, Baltimore and Howard counties all border parts of the Patapsco River and rely on Baltimore City’s Patapsco Wastewater Treatment Plant — it’s not clear whether other communities may be impacted by the capacity crunch.

Howard County spokesperson Safa Hira said sewage from nearby areas of its jurisdiction feed into Baltimore’s Patapsco treatment plant but remain “well below” sewage flow limits.

In light of Anne Arundel County’s announcement, though, Hira said Howard County officials are coordinating with Baltimore “to better understand the situation.”

Banner reporter Lillian Reed contributed to this story.

This story has been updated.