Florida didn’t just build the “Alligator Alcatraz” migrant detention facility. The state is also responsible for deciding which illegal immigrants to hold there, the federal government said Thursday.

Thomas Giles, a senior official at U.S. Immigration and Customs Enforcement, said ICE’s only involvement in the project has been touring the site in the Everglades to make sure it complies with federal standards and meeting with state officials “to discuss operational matters.”

“The ultimate decision of who to detain at the [Training and Transition Airport] Detention Facility belongs to Florida,” he told a federal judge in a filing.

He said the migrants would be detained under Florida’s powers under a 287(g) agreement with the federal government. That program lets state and local authorities detain — and in some cases arrest — deportation targets under U.S. immigration laws.

The Justice Department is trying to help Florida fend off a federal lawsuit challenging the facility under environmental law.

Friends of the Everglades said the project should have gone through an environmental assessment before being launched.

The group said the detention facility will trouble endangered species, including the Florida panther.

But federal officials say the environmental rules under which the challengers are suing apply only to federal projects.

Hence, ICE’s argument that the facility is under Florida’s control.

“Plaintiffs fail to identify any final agency action by a federal defendant. DHS has not implemented, authorized, directed or funded Florida’s temporary detention center,” the Justice Department said.

Mr. Giles said ICE did not pay for construction and has not paid to rent any detention space at the Dade-Collier Training and Transition Airport, which is where the tent facility has been set up.

An official from the Federal Emergency Management Agency said it does plan to reimburse Florida out of its Detention Support Grant Program.

• Stephen Dinan can be reached at sdinan@washingtontimes.com.