A sprawling marijuana plantation with an estimated 30,000 plants near Mountain Creek Lake was discovered Wednesday in what may be one of the largest such finds in the southern United States, Dallas police said.

Officers spotted the field from the air, but Drug Enforcement agents were unable to reach the area on foot Wednesday.

DEA spokeswoman Terri Wyatt said she could not confirm the estimated size of the crop until authorities were able to survey the site by ground. But Dallas police officials confirmed to The Dallas Morning News and WFAA-TV the estimated number of plants, which could be worth $20 million to $25 million on the street. That amount would dwarf the previous record haul uprooted last month in the same area.

"It's huge. It's probably going to be the biggest one [ever] in Dallas County," said one Dallas police official, who like others spoke on the condition that he not be named.

If confirmed, the haul would rival some of the nation's largest recent marijuana plant seizures. Last month, Chicago DEA agents helped remove 38,000 plants from 14 fields inside the Crabtree Nature Preserve in Barrington, Ill.

In 2004, Washington officials seized about 65,000 marijuana plants worth nearly $35 million from an American Indian reservation in Klickitat County, Wash.

Three of the four recent large outdoor pot caches discovered in North Texas have been in the Mountain Creek area near the Dallas-Grand Prairie border, including the previous record haul of 10,451 plants found last month.

An Oklahoma Army National Guard helicopter helped investigators clear those plants from land near Grand Prairie's Ronald W. Reagan Middle School on terrain too treacherous for an all-terrain vehicle.

On Sunday, police discovered about 1,600 more plants in the same area near Interstate 20 and Spur 408.

"A crop of this magnitude is more than likely the result of a Mexican drug cartel," Special Agent Wyatt said. "Only time and more evidence and more leads and more investigating will prove or disprove that."

Special Agent Wyatt said the fields around the lake are probably run by the same group, without the knowledge of landowners. No arrests have been made.

"There's still a lot to be done with the leads that we have," she said.

Another marijuana field was uncovered last month just a few hundred yards behind the regional DEA and FBI headquarters on Stemmons Freeway. That site contained about 325 plants, some 12 feet tall, on plots carved out of the woods near the Trinity River.

Special Agent Wyatt called the number of recent finds unusual, but said data analyzed over the last decade show no trend in the volume of marijuana seized locally.

She said heightened vigilance and public awareness after the first fields were found have helped uncover others.

"Everybody's on the lookout," she said.

Staff writer Tanya Eiserer and Rebecca Lopez of WFAA-TV contributed to this report.