A March 22 collision of two ships resulted in an oil spill that closed a major U.S. shipping channel for days, killed wildlife, and caused the evacuation of a nearby dike—not to mention dumping around 168,000 gallons of oil into Galveston Bay. Perhaps most disturbing, though, are the crowded conditions that led to the accident.

It was a foggy late morning in the Houston Ship Channel when a tugboat towing two barges made way for a large bulk carrier ship. Despite a call between ship captains about five minutes before the incident, a collision was unavoidable.

“If you keep on going, I'm going to get you,” the captain of the bulk carrier, said in a recording of the call, according to the Associated Press. “Captain, I can cut her back. I can go dead slow, but that still ain't going to stop it because I'm coming up on half a mile of you.”

The tugboat, which was hauling nearly a million gallons of a thick form of oil known as bunker fuel, tried to back out of the channel, but it was too late, according to the AP report. The resulting collision partially submerged the barge and allowed 168,000 gallons, or about 4,000 barrels, of oil to escape.

The Houston channel was closed for nearly six days while crews worked to clean up the spill. Industry experts worried about the nationwide impacts of cutting off one of the busiest petrochemical ports in the United States from the Gulf of Mexico, while wildlife officials fretted over the pollution of an important shorebird habitat during the peak of migration season. The Texas City Dike was closed as black globs of oil appeared on its shores and oil tarnished the popular Padre Island, as well.

Despite the far-reaching impacts of the accident, which the U.S. Coast Guard called a significant spill, lies the import of the crowded ship channel that moves about 80 ships a day along with hundreds of tugboats and barges. Accident numbers for the channel weren’t readily available, but a 2012 National Transportation Safety Board investigation into another collision cited traffic in the channel as problematic in waterway with a limited margin for error.

“The only thing I can say is, ‘Wow,’” Tim Gunn, tugboat captain for Buffalo Marine Service Inc., told Bloomberg News in 2013. “Sometimes you can meet and be overtaken by a handful of ships, 10 to 15 of them. When I first started it seemed like two or three.”

While traffic in the channel has increased along with energy demands, infrastructure maintenance has not, leading to dangerous conditions. Federal funding cuts have made it difficult to keep up with the dredging needed to keep the channel clear, according to Bloomberg. Along with that, natural flow conditions in the channel make it difficult to pilot as well, the NTSB report said.

The combination can lead to near misses and full-on hits like the March collision. Just days earlier, a similar spill was avoided when a cargo ship carrying rice collided with a barge carrying thousands of gallons of oil, according to the Houston Chronicle.

Although crowded conditions in the channel aren’t likely to dissipate, an estimated $35 billion in capital and maintenance projects is underway, according to Bloomberg. The question remains, however, whether the projects will keep up with the demands from the companies that rely on the port—and whether the change will happen quickly enough.

“We’re still trying to stuff these bigger ships up these tiny ditches,” Captain Mike Morris, presiding officer of the Houston Pilots, told Bloomberg. “Everywhere you look in the port, we’re expanding.”