Millions of homes in the U.S. are harboring a hidden drowning danger for kids in their backyards. This week, the U.S. Consumer Product Safety Commission announced a massive recall of certain backyard pools that have already caused the deaths of several children.

The CPSC issued the recall on Monday in conjunction with multiple backyard pool manufacturers. The recalled pools—five million in total—all carry compression straps that make it possible for small kids to enter the structure without their parents or other caregivers noticing. At least nine drowning deaths of children between the ages of 22 months and 3 years old in six states have been associated with the products since 2007.

The recall specifically concerns 48-inch and taller above-ground pools with compression straps sold by the companies Bestway, Intex, and Polygroup. The compression straps are wrapped around the pool on the outside of the supporting poles to further secure its structural integrity. But children can use the straps as a foothold to get inside the pool even with the ladder removed, the CPSC said, heightening the risk of unattended swimming and drowning. In addition to the nine deaths, the CPSC has documented three other incidents in which children entered the pools via the straps.

These pools were originally manufactured in China and have been sold across the U.S. since 2002 at various nationwide chains, including Walmart, Target, Sears, and Toys “R” Us, as well as at online retailers like Amazon. About 266,000 of these pools were also sold in Canada. A full list of the recalled products can be seen here, and the pool brand names and model numbers can be found on the pool liner on the pool’s exterior.

People who own the recalled pools are advised to contact the manufacturers. They can obtain a free repair kit containing a rope designed to wrap around the pool and attach to its vertical support poles at ground level, effectively replacing the function of the compression straps. People should first install the repair kit before cutting and removing the straps, the CPSC said. Until the kit is secured, the agency added, families should ensure their children can’t access the pool when unattended or simply drain the pool to prevent use.

The CPSC is also reminding people to practice good pool safety for themselves and their children in general. Though rare, about 350 children under five are estimated to die each year in the U.S. from drowning in pools, according to the agency.