A film crew working on a documentary for public television has arrived in Birmingham to film day and night in Bibb County, south of Birmingham, hoping to capture a rare water lily as it flowers and is pollinated by moths on the Cahaba River.

Grizzly Creek Films, a production company based in Bozeman, Montana, has a crew in Alabama this week working on a documentary about the Cahaba lilies. The filming is taking place in the Cahaba River National Wildlife Refuge in West Blocton.

The Cahaba lilies, which appear between Mother’s Day and Father’s Day, are in full bloom right now.

“They’re gorgeous this year,” said Beth Stewart, executive director of the Cahaba River Society. “We have the largest stand of Cahaba lilies in the world.”

The picturesque nature-scape of the white lilies in mid-stream has attracted the attention of the filmmakers from Montana.

“They’re making a documentary about the Cahaba lilies right now,” she said. “We’re going to be helping them. They’re going to be doing filming both during the day and at night because they want to try to capture pollination.”

The moon will be full on Thursday, and this week’s moonlight illuminates a hidden drama on the river.

“The lilies are night-pollinated,” Stewart said. “A couple of years ago we did a moonlight canoe trip, the only time we did an official one, because it’s a little scary to be out on those shoals in the dark. You can’t see where the bottom of the river is. You can’t see the rocks.”

What mostly goes unseen is the dance of moths on the moonlit lilies.

“The lilies are made for nighttime pollinations,” Stewart said. “At night, they are just blazing white. They exude this amazing dew that completely dots the inside and outside of the flowers and carries the scent of the lilies on it. The whole shoals just smells fabulous at night. That’s when these sphinx moths and other pollinators, but mainly these moths that are huge and have a really long proboscis, that’s when they come and pollinate. The PBS crew is trying to capture that.”

On Sunday, dozens of people drove their cars down a single-lane dirt road called River Road, at the bridge at Bibb County 24 near West Blocton, parked up against the weeds on the gravel, then waded out into the river to get photos of the large groves of Cahaba lilies growing in the middle of the river.

“That’s the largest Cahaba lily stand on earth,” Stewart said. “They’re called the Cahaba lily or the Shoals spider lily. They’re in South Carolina and Georgia too. We’ve got the most.”

The lilies are very particular about where they grow. They take root in the rocks of the fast-flowing river.

“They won’t grow if they’re not in a river, in running water in that particular habitat,” Stewart said. “People used to try to dig them up, take them home and put them in their garden. They won’t grow. They’ll just die. There’s a different species, called the swamp lily, or the Carolina lily, that looks a lot like the Cahaba lily. That will grow in a garden. It’s made for damp or swampy ground. It’s a different species and sometimes those are available in garden stores. That’s the only one that could work in a garden.”

Cahaba lilies can only grow wild.

“Cahaba lilies, the seeds sink,” she said. “They have to sink and wedge themselves in the crevices of the shoals of the rocks, and then they root. They will not grow unless there’s running water over them.”

They have banner years and less so, sometimes based on how development in the metro area affects stormwater flow into the river.

“The lilies are an indicator of the health of the river,” Stewart said.

“They’re threatened by everything that’s going on in the way that we’ve altered the flow of the river because of all the development in Birmingham metro area because we have so much more storm water runoff, because we have higher floods, more intense floods,” Stewart said. “That carries big chunks of trees that go through the lilies like a bulldozer. There’s also a lot of sediment from all of the extra stormwater flow. The Cahaba River has to get bigger because it’s carrying more rainwater on a regular basis every time it rains. That’s why the banks are collapsing. That’s why we see so much sediment. That’s why the river’s so brown after it rains.”

But right now, the lilies are fabulous. “They are beautiful right now,” Stewart said.

For details and tips on viewing the Cahaba lilies, check out the Cahaba River Society’s website.