They’re building a new lighthouse in south Texas, but it’s not on the Gulf Coast. In fact, it’s nowhere near a major body of water.

Instead, the 70-ft-tall structure is the visual centerpiece of a charity effort to build a unique water park. The project is being organized and overseen by the Associated General Contractors of America as part of its annual convention, which opens today and runs through March 11 in San Antonio.

The association’s charity organization, AGC Charities Inc., and dozens of construction firms from San Antonio and across the country have launched a volunteer project to build Morgan’s Inspiration Island. It will become an ultra-accessible water park, an addition to the nonprofit Morgan’s Wonderland theme park in San Antonio.

Led by general contractor Linbeck Group and AGC of San Antonio as part of the AGC Charities’ annual Operation Opening Doors program, the firms are donating time, expertise and money to build the key vertical components of the park by the end of March.

“Nothing our group has done before this has come close to the size, scope and ambition of this project,” said Scott Williams, president of Springfield, Ore.-based Hamilton Construction Co. and chairman of AGC Charities, in a statement. “These contractors are making sure every child has an opportunity to have fun and enjoy a day at a water park.”

AGC Charities and the local contractors, who call themselves the Morgan’s Inspiration Island Working Group, are building five new pump houses, a main building and the signature lighthouse feature for the special needs-accessible water park, Williams noted.  The total value of construction services being donated is more than $400,000, AGC said.

The volunteer contractors are doing most of the construction work during a weeklong blitz that started March 7.

“The easiest part has been finding contractors willing to donate their services to make this project a reality,” says Patrick Byrnes, a senior cost analyst with Linbeck, who is serving as project manager for the operation. “Contractors are eager to help build something that will allow every child to splash around and have fun without having to worry about the challenges they may face.”

According to park officials, Morgan’s Wonderland is the world’s first theme park designed with special-needs individuals in mind. The new expansion to Morgan’s Wonderland, called Morgan’s Inspiration Island, is scheduled to open in spring 2017. The park addition will include five new water “splash-pad” areas and a lazy-river boat ride.

But the job has faced some difficulties. Because the AGC-member firms are building only the vertical components of the six-acre theme park—with the park itself tackling installation of the water features and tenant finish of the main building later—the schedule has become an “inverted fast-track sprint,” Byrnes says, referring to doing the buildings before completion of all utilities and sitework. As of Monday, crews had completed 20% to 25% of the total AGC-led scope, he says, with a target of 40% completion by the end of the week.

Delayed delivery of key materials such as the roof trusses have forced crews to scramble for workarounds, and early site excavation for the pump houses hit “unlocated underground utilities,” including a 24-in. main sewer line that serves restroom facilities at nearby ball fields, Byrne says.

“We thought this section [the water-park portion] was a greenfield site,” says Chuck Davis, the park’s construction superintendent. “It isn’t.”

Still, Byrne says that crews have “done a great job” of coordinating their work on the tight site and navigating simultaneous construction of the pump houses and the main concessions and guest-prep building that connects to the lighthouse.

“We are deeply grateful for AGC Charities’ enthusiastic commitment to help build another world-class place of inclusion,” said philanthropist Gordon Hartman in a statement. He spearheaded creation of Morgan’s Wonderland in 2010.  “Just like Morgan’s Wonderland, Morgan’s Inspiration Island guests, with and without special needs, will be able to come together for fun and a better understanding of each other.”

A number of San Antonio-based firms are participating in the Morgan’s Inspiration Island Working Group, Byrnes says.  In addition to Linbeck Group, the other firms include: Allegiance Crane, Alterman Inc., Architectural Division 8, Baker Triangle, Beldon Roofing, Commercial Hardware, F.A. Nunnelly Co., Galaxy Builders, Guido Materials, Joeris General Contractors, Marek Brothers Systems Inc., Martin Marietta, MBCI, RSG, Safety Supply, Sherwin Williams, Southwest Exteriors, Sunstate Equipment Co., Texas Air Products, Turner Roofing and YouthBuild.