The mayors of Newport Beach and Laguna Beach will face off Friday to see whose city is more water-wise in a month-long national online competition.

Mayors Nancy Gardner of Newport and Jane Egly of Laguna will kick off the National Mayor's Challenge for Water Conservation from 3 to 4 p.m. at the Back Bay Science Center, 600 Shellmaker Road, Newport Beach.

Environmental artist Wyland and Environmental Protection Agency water office head Nancy Stoner will also be in attendance.

"They're going down," Gardner quipped of Laguna Beach on Thursday. "Newport has really been on top of water issues for so long. We early on made the connection between water conservation and water quality."

As for her plans to win, "I'm going to arm wrestle all the other mayors," she joked. "Once we get it kicked off, I'll start thinking of some things I can do. I'll share those ideas in my newsletter."

A link to her webpage and newsletter can be found on the city's website.

"We're No. 1," she said.

Celebrating the 40th anniversary of the Clean Water Act, the program encourages residents to conserve water and reduce pollution into local watersheds, according to a news release.

Residents in the winning cities could win a Toyota Prius, a custom-designed sprinkler system from Rain Bird, EcoFlow showerheads from WaterPik, Sterling water-saving toilets and gift cards from Lowe's Home Improvement stores.

Cities will be divided into four regions — West, Midwest, South and Northeast — and categorized by population. Cities with the highest percentage of residents participating in the challenge win.

For more information or to sign up, visit http://www.mywaterpledge.com.

jamie.rowe@latimes.com

Twitter: @jamierowe3