About 3,000 subscribers of the My Waste app may have had their email addresses accessed, the region says.
The owner of the My Waste app, Recycle Coach, was compromised in a larger, worldwide issue, the region said in a release Friday.
App users who had their email addresses accessed on April 16 were told of the information breach on Thursday.
"The only information accessed was email addresses. No passwords, names, addresses, location or country information were compromised," the region said.
"Some subscribers may receive or continue to receive spam email as a result of this incident."
The My Waste app informs users about their waste pickup schedule and offers tips on recycling and other waste issues.
Users who opted in to receive marketing information from Recycle Coach and My Waste were the only ones affected. There are more than 38,000 residents in Waterloo region who use the app.
"Recycle Coach has assured the Region that it is taking steps to improve their security measures to better protect user information," the region said.
Recycle Coach, which is based in Toronto, said in total, 55,000 emails that were part of an email list hosted on MailChimp were exposed.
The emails were exposed Monday at 6:15 p.m. ET.
"Though no names, location information, or passwords were exposed, we know we have to do better. And we will," the company said in a blog post.