Heat and humidity return to southern Ontario

Nicole, 8, plays at a splashpad in Breslau, Ont. on July 2, 2026. (Heather Senoran/CTV News)

Another heat event has been declared in southwestern Ontario.

Environment Canada said temperatures could climb to 37 degrees Celsius on Tuesday.

With the humidex, it will likely feel closer to 38 or even 45.

“Tuesday will mark the peak of this heat event,” the alert said.

Environment Canada said the high heat is expected to continue until late Wednesday or Thursday.

Almost all of the province was under a heat warning on Monday afternoon.

Signs of heat illness

Heat illness is a serious concern when the mercury rises, especially in older adults, infants, young children, pregnant people, those with physical or mental illnesses, mobility issues, people who work outside and the homeless community.

Symptoms of heat exhaustion include:

• Headache
• Nausea or vomiting
• Dizziness or fainting
• Extreme thirst
• Dark urine and decreased urination
• Intense fatigue
• Confusion or lack of coordination
• Skin rash
• Muscle cramps
• Heavy sweating
• Rapid breathing and heartbeat

Heat stroke, by comparison, is considered a medical emergency.

Symptoms include:

• High body temperature
• Very hot, red skin
• Confusion or change in consciousness
• Dizziness or fainting
• No sweating

If someone is experiencing heat stroke, experts advise moving them to a cool place, giving them water and placing ice packs on their body. Call 911 immediately.

Beating the heat

The key to avoiding heat illness is to plan ahead.

Here are a few things to keep in mind:

• Know the weather forecast before going outside
• Modify your plans according to the weather
• Drink plenty of cool liquids, especially water, even before you feel thirsty
• Avoid drinks that are high in sugar, caffeine or alcohol
• Wear loose-fitting, light-coloured clothing made of breathable fabric
• Seek shade
• Avoid sun exposure if you can
• Take breaks as needed
• Avoid using your oven
• Take a cool shower or bath
• Take a break by spending a few hours in a cool place
• Close blinds and shades,
• Turn on air conditioning or use a fan

Cooling centres

The best way to get relief from the heat and humidity is to seek out a designated cooling centre.

The Region of Waterloo has locations listed on their website. They include libraries, community centres, museums and regional offices.

The map also includes a list of public swimming pools and splash pads.

Protecting your pets

Never leave pets inside a hot vehicle.

Dogs can also experience heatstroke, and it could lead to organ failure or even death.

Signs of an overheated pet include:

• Excessive panting
• Drooling
• Vomiting
• Collapsing
• Lethargy
• Tongue can appear red or hang out of their mouth

If your pet is suffering from the heat, it’s a good idea to gradually cool them down. Experts suggest using a cool blanket or towel that is wet. Avoid using ice.

Owners should keep pets at home when the temperature climbs but if they need to go outside, keep them off the pavement as much as possible, only go for a short walk, or take them out in the morning or evening when it’s cooler.

Anyone concerned about the well-being of an animal is advised to call 911.

Outdoor workers

The City of Waterloo wants to make sure crews who work outdoors are being safe in this heat. That includes city staff who maintain gardens, transportation workers and utility workers.

“We have to ensure that we remind staff of the taking of extra breaks and ensuring that they are consuming enough water. I think it can be easy to get lost in the work that you’re doing,” Kathy Weidhaas, director of human resources at the City of Waterloo, said.

The Region of Waterloo said construction and infrastructure work generally continues during periods of extreme heat.

“Crews follow established health and safety procedures and work activities or schedules may be adjusted as needed to accommodate weather conditions,” a spokesperson for the region said in a statement. “These kinds of adjustments are a normal part of managing outdoor work safely while maintaining essential projects and services.”

Indoor safety

Climate experts said it isn’t just the temperature outdoors that people should be worried about.

“In 2021, B.C. had a heat dome that killed 619 people. Ninety-eight per cent of those deaths were indoors,” said Anabela Bonada, from the Centre for Climate Adaptation with the University of Waterloo.

A lack of air conditioning or adequate air flow can be deadly.

“We have new guidance from Health Canada that states that 26° Celcius should be the absolute maximum indoor temperature,” Bonada said.

Bonada believes municipalities should implement bylaws to ensure landlords guarantee a maximum internal temperature in rentals.

“We currently have that for the winter. So, landlords must provide a minimum indoor temperature during the winter,” she said. “Starting that off would be bylaw first and then enforcement. This all takes time. I absolutely think we need to accelerate this as we’re already experiencing extreme heat.”

The City of Waterloo and the City of Cambridge said there are no plans to change any bylaws about maximum temperature at this time. But both cities said property standards bylaws require rental units to be safely maintained, including keeping any provided air conditioning in working order.