In 1976, two college students died while exploring the “Blue Hole,” an underwater cave connected to a deep lake in Santa Rosa, N.M. Shortly thereafter, local officials poured rubble and boulders into the bottom of the pool and sealed it off with a grate to prevent any more amateur divers from entering the cave. The ploy worked — all too well.

Beginning this past Friday, a team of experienced divers attempted to enter the cave and map it for the first time, although rough sketches of the cave were made by police divers in the 1970s, said Walter Pickel, part of the current team.

The team spent several days excavating the rubble and removing the gate, and one diver was able to get into an “antechamber” about the size of a car’s front seat. But a large boulder kept the explorers from entering the cave, said Pickel, a diver and logistics officer for Advanced Diver Magazine. A connection into the larger cave was made, but the passageway is too small to crawl through, he said.

“We can see into it; it’s taunting us,” Pickel said. “But it’s impassable.”

However, there was some upside — the excavation has allowed more water to flow from underground into the Blue Hole, which pours into a spillway that provides water for local farmers. “That made them happy,” Pickel said. Now that water is flowing more quickly, the lake has also become more clear, since the current carries away sediment more quickly, he said.

“With respect to the cave exploration, our team was disappointed,” he said. “But you have to find a silver lining.”

The lake is actually a type of artesian well, in which pressurized water seeps up from below, said Richard Delgado, the tourism director for the city of Santa Rosa. Delgado said he wagers it’s connected to other caves in the area, which is known for having several deep lakes consisting of flooded caverns.

The ADM team travels to caves around the world, often getting permission from private landowners to enter their caves. In return, ADM makes maps of what’s inside them, Pickel said. The team has no concrete plans to explore the Blue Hole cavern again, but Pickel said they might come back if the town gets funding to remove the boulder blocking the way. The team next hopes to explore a cave in Belize.

The Blue Hole was formerly a sinkhole caused by the dissolution of underground limestone and gypsum, according to the New Mexico Bureau of Geology and Mineral Resources. Many of the area’s caves and sinkholes were formed by the same process. Groundwater is plentiful in the region, as it lies on the western edge of the Ogallala Aquifer, Delgado said.