THOUSAND OAKS, Calif. (AP) — Authorities say 19 children were sickened by exposure to a chemical at a Southern California swimming pool.
The Ventura County Fire Department says the swimmers were overcome by fumes Wednesday evening at Daland Swim School in Thousand Oaks, north of Los Angeles.
Some reported having trouble breathing but their problems are non-life-threatening.
Photos of the week: 9/21 - 9/28
Photos of the week: 9/21 - 9/28
WASHINGTON, DC - SEPTEMBER 27: Judge Brett Kavanaugh testifies to the Senate Judiciary Committee during his Supreme Court confirmation hearing in the Dirksen Senate Office Building on Capitol Hill September 27, 2018 in Washington, DC. Kavanaugh was called back to testify about claims by Christine Blasey Ford, who has accused him of sexually assaulting her during a party in 1982 when they were high school students in suburban Maryland. (Photo by Win McNamee/Getty Images)
Actor and comedian Bill Cosby leaves the Montgomery County Courthouse after sentencing in his sexual assault trial in Norristown, Pennsylvania, U.S., September 25, 2018. REUTERS/Brendan McDermid TPX IMAGES OF THE DAY
WASHINGTON, DC - SEPTEMBER 27: Christine Blasey Ford testifies before the Senate Judiciary Committee in the Dirksen Senate Office Building on Capitol Hill September 27, 2018 in Washington, DC. A professor at Palo Alto University and a research psychologist at the Stanford University School of Medicine, Ford has accused Supreme Court nominee Judge Brett Kavanaugh of sexually assaulting her during a party in 1982 when they were high school students in suburban Maryland. (Photo by Win McNamee/Getty Images)
U.S. President Donald Trump addresses the 73rd session of the United Nations General Assembly at U.N. headquarters in New York, U.S., September 25, 2018. REUTERS/Carlo Allegri
BUCKSPORT, SC - SEPTEMBER 26: An antique car is inundated by floodwaters from the Waccamaw River caused by Hurricane Florence on September 26, 2018 in Bucksport, South Carolina. Nearly two weeks after making landfall in North Carolina, river flooding continues after Florence in northeastern South Carolina. (Photo by Sean Rayford/Getty Images)
Palestinian cadets crawl as they demonstrate their skills at a police college run by the Hamas-led interior ministry, in Khan Younis in the southern Gaza Strip, September 26, 2018. REUTERS/Mohammed Salem TPX IMAGES OF THE DAY
Senate Judiciary Committee member Sen. Lindsey Graham (R-SC) shouts while questioning Judge Brett Kavanaugh during his Supreme Court confirmation hearing in the Dirksen Senate Office Building on Capitol Hill in Washington, U.S., September 27, 2018. Win McNamee/Pool via REUTERS TPX IMAGES OF THE DAY
TOPSHOT - Venezuelan migrants have their hair cut by a social brigade from the local government, near a bus terminal, in Bogota on September 26, 2018. (Photo by John VIZCAINO / AFP) (Photo credit should read JOHN VIZCAINO/AFP/Getty Images)
Britain's Meghan, The Duchess of Sussex, rubs noses with a guest, as a traditional Maori greeting, at the opening of 'Oceania' at the Royal Academy of Arts in London, Britain, September 25, 2018. Picture taken September 25, 2018. Arthur Edwards/Pool via REUTERS TPX IMAGES OF THE DAY
New Zealand Prime Minister Jacinda Ardern kisses her baby Neve after speaking at the Nelson Mandela Peace Summit during the 73rd United Nations General Assembly in New York, U.S., September 24, 2018. REUTERS/Carlo Allegri
CONWAY, SC - SEPTEMBER 23: People navigate floodwaters caused by Hurricane Florence near the Waccamaw River on September 23, 2018 in Conway, South Carolina. Floodwaters are expected to continue to rise in Conway over the next two days. (Photo by Sean Rayford/Getty Images)
Ethnic Miao women in traditional costumes take part in a tug of war to celebrate a local festival at a village in Rongshui Miao Autonomous County, Guangxi Zhuang Autonomous Region, China September 27, 2018. Picture taken September 27, 2018. REUTERS/Stringer ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. CHINA OUT. TPX IMAGES OF THE DAY
WASHINGTON, DC - SEPTEMBER 27: Senate Judiciary Committee member Sen. Patrick Leahy (D-VT) questions Judge Brett Kavanaugh during his Supreme Court confirmation hearing in the Dirksen Senate Office Building on Capitol Hill September 27, 2018 in Washington, DC. Kavanaugh was called back to testify about claims by Christine Blasey Ford, who has accused him of sexually assaulting her during a party in 1982 when they were high school students in suburban Maryland. (Photo by Win McNamee/Getty Images)
Volunteers arrange the coffins containing the dead bodies of passengers retrieved after a ferry MV Nyerere overturned off the shores of Ukara Island in Lake Victoria, Tanzania September 22, 2018. REUTERS/Jackson Njehia TPX IMAGES OF THE DAY
CHICAGO, IL - SEPTEMBER 20: Eleven-year-old Sofia Sanchez gives a hug to Dr. Osama Eltayeb following a press conference which she attended with her heart surgery team to discuss her recent heart transplant at the Ann & Robert Lurie Children's Hospital of Chicago on September 20, 2018 in Chicago, Illinois. Sanchez grabbed national attention while in the hospital waiting for her transplant by making a video to convince Canadian pop star Drake to visit her. Drake spent about 90 minutes visiting with Sanchez while he was in Chicago to perform at a concert. (Photo by Scott Olson/Getty Images)
UNITED STATES - SEPT 27: Joy Gerhard, of Seattle, cries in the Hart Senate Office Building atrium as she listens on her phone to Dr. Christine Blasey Ford testify on the sexual assault by Supreme Court nominee Brett Kavanaugh, Thursday Sept. 27, 2018. (Photo By Sarah Silbiger/CQ Roll Call)
A United States Marines V-22 Osprey helicopter carrying members of the press following President Donald Trump is seen as Trump traveled from New Jersey to Manhattan in New York City, New York, U.S., September 23, 2018. REUTERS/Mike Segar TPX IMAGES OF THE DAY
Male deers run in a field in Republican landscape reserve "Naliboksky" near the village of Kozliki, Belarus September 23, 2018. REUTERS/Vasily Fedosenko TPX IMAGES OF THE DAY
Students cross a bamboo bridge, above a garbage-filled stream branching off the Ciliwung River, in Bogor, Indonesia, September 25, 2018. Picture taken September 25, 2018. Antara Foto/Yulius Satria Wijaya via REUTERS - ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. MANDATORY CREDIT. INDONESIA OUT. NO COMMERCIAL OR EDITORIAL SALES IN INDONESIA. TPX IMAGES OF THE DAY
Sunni Welles, 70, who has accused actor and comedian Bill Cosby of sexually assaulting her when she was 17, reacts at a press conference following his sentencing, in Norristown, Pennsylvania, U.S., September 25, 2018. REUTERS/Jessica Kourkounis TPX IMAGES OF THE DAY
People look at the damage after a tornado hit the Mont-Bleu neighbourhood in Gatineau, Quebec, Canada, September 22, 2018. REUTERS/Chris Wattie TPX IMAGES OF THE DAY
CHENGDU, CHINA - SEPTEMBER 24: A Giant Panda eats bamboo at the Chengdu Giant Panda Breeding Research Base on September 24, 2018 in Chengdu, China. (Photo by Zhong Zhi/Getty Images)
WASHINGTON, DC - SEPTEMBER 26: U.S. Supreme Court Justice Ruth Bader Ginsburg (R) waves to students as she arrives at a lecture September 26, 2018 at Georgetown University Law Center in Washington, DC. Justice Ginsburg discussed Supreme Court cases from the 2017-2018 term at the lecture. (Photo by Alex Wong/Getty Images)
SYDNEY, AUSTRALIA - SEPTEMBER 24: A woman looks at a whale carcass on Wattamolla Beach in the Royal National Park south of Sydney on September 24, 2018 in Sydney, Australia. The carcass is believed to be a rare Sei whale. (Photo by Jenny Evans/Getty Images)
Demonstrators chant before being arrested as they protest against U.S. Supreme Court nominee Brett Kavanaugh in front of the office of Senator Susan Collins (R-ME) on Capitol Hill in Washington, U.S., September 24, 2018. REUTERS/Joshua Roberts TPX IMAGES OF THE DAY
CHUUK, FEDERATED STATES OF MIRCONESIA - SEPTEMBER 28: U.S. Navy Sailors from Underwater Construction Team (UCT) 2 assist local authorities in shuttling the passengers and crew of Air Niugini flight PX56 to shore following the plane crashing into the sea on its approach to Chuuk International Airport on September 28, 2018 in the Federated States of Micronesia. (Photo by Lt. Zach Niezgodski/U.S. Navy via Getty Images)
PHILADELPHIA, PA - SEPTEMBER 21: Former President Barack Obama greets supporters after he spoke during a campaign rally for Senator Bob Casey (D- PA) and Pennsylvania Governor Tom Wolf on September 21, 2018 in Philadelphia, Pennsylvania. Midterm election day is November 6th. (Photo by Mark Makela/Getty Images)
Tristan Robertson-Eyes, aged 7, plays with Elasti Plasti at the launch of Hamleys top Christmas toys, in London, Britain, September 26, 2018. REUTERS/Peter Nicholls TPX IMAGES OF THE DAY
Former model Janice Dickinson returns to the courtroom during the lunch break in the sexual assault trial sentencing hearing for entertainer Bill Cosby at the Montgomery County Courthouse in Norristown, Pennsylvania, U.S. September 24, 2018. David Maialetti/Pool via REUTERS TPX IMAGES OF THE DAY
A search team walks down Tulip Drive in Gastonia, N.C., Wednesday, Sept. 26, 2018. Local law enforcement officers, fire and rescue personnel, and the FBI continue to look for clues to the whereabouts of 6-year-old Maddox Ritch who disappeared from Rankin Lake Park near downtown Gastonia, on Saturday, Sept. 22. (John Clark /The Gaston Gazette via AP)
ATTENTION EDITORS - VISUAL COVERAGE OF SCENES OF INJURY OR DEATH Rescuers carry a survivor amidst the rubble after a building collapsed in New Delhi, India, September 26, 2018. REUTERS/Adnan Abidi TEMPLATE OUT TPX IMAGES OF THE DAY
KONYA, TURKEY - SEPTEMBER 28: A drone photo shows one of the potholes that increase in recent years at Karapinar district of Konya, Turkey on September 28, 2018. Consisting of decreased ground water level based on increasing of agricultural activities, concern residents in the area.
(Photo by Abdullah Coskun/Anadolu Agency/Getty Images)
Actor and comedian Bill Cosby is seen in this booking photo released by State Correctional Institute Phoenix in Collegeville, Pennsylvania, U.S., September 26, 2018. SCI Phoenix/Pennsylvania Department of Corrections/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY.
Smoke rises from the construction site of the headquarters of the National Bank of Kuwait, September 27, 2018. REUTERS/Stephanie Mcgehee TPX IMAGES OF THE DAY
SALT LAKE CITY, UT - SEPTEMBER 26: Professor Anita Hill gets a standing ovation as she arrives for a speech to students, faculty and guests on the campus of the University of Utah on September 26, 2018 in Salt Lake City, Utah. Hill who was involved in the hearing for Supreme Court Justices Clarence Thomas in 1991, will give a speech entitled 'From Social Movement, To Social Impact'. (Photo by George Frey/Getty Images)
Labourers work in front of a giant sculpture of a man wearing a gas mask that will be used to decorate an "Open Air" themed pandal (temporary platform) for the upcoming Hindu festival of Durga Puja in Kolkata, India, September 28, 2018. According to organizers, the theme of the pandal seeks to create awareness on the importance of clean, unpolluted air, to devotees of Goddess Durga. REUTERS/Rupak De Chowdhuri TPX IMAGES OF THE DAY
LAS VEGAS, NV - SEPTEMBER 23: Former first lady Michelle Obama greets supporters after speaking at a rally for When We All Vote's National Week of Action at Chaparral High School on September 23, 2018 in Las Vegas, Nevada. Obama is the founder and a co-chairwoman of the organization that aims to help people register and to vote. Early voting for the 2018 midterm elections in Nevada begins on October 20. (Photo by Ethan Miller/Getty Images)
AITOLIKO, GREECE - SEPTEMBER 24: Gigantic spider web covers an area of greenery along the coast of Aitoliko, Greece on September 24, 2018. High temperatures in western Greece helped create ideal conditions for the creation of the spiderweb.
(Photo by Ayhan Mehmet/Anadolu Agency/Getty Images)
Devotees splash water on an idol of Hindu elephant god Ganesh, the deity of prosperity, as it is carried for immersion into the Arabian Sea on the last day of the Ganesh Chaturthi festival in Mumbai, India, September 23, 2018. REUTERS/Danish Siddiqui TPX IMAGES OF THE DAY
LEEDS, ENGLAND - SEPTEMBER 22: Prince Charles, Prince of Wales poses for a group photo with members of the Queen's own Yeomanry at a Consecration Service at Bramham Park on September 22, 2018 in Leeds, England where he presented a new guidon to the Queen's own Yeomanry. (Photo by Richard Martin-Roberts/Getty Images)
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A dozen children, aged between 11 and 15, were taken to hospitals, including several who at first were described as being in a critical state.
However, sheriff's officials say all are expected to recover.
The Los Angeles Times says authorities believe an equipment malfunction began pumping extra chlorine into the pool.
A call to the swim school wasn't immediately returned.