Jan
2026
14
Can Algae Grow in a Closed Pool During Winter?
During the winter, pool owners don’t really have direct access to their swimming pool water and are not spending a lot of time outside. As your pool sits outside through the winter months, algae can actually grow in your pool even if it is closed. This can sometimes happen with DIY pool closing or when the balance of pool supplies and chemicals used is just off. The good news is that with professional pool maintenance and guidance from a reputable service company, you can rid your pool of algae when it’s time to open. Reach out to Seaway Pools & Hot Tubs’ pool builders in Whitby to start building your dream pool or book a service for your existing pool or hot tub online.
What is Algae?
Algae are plant-like organisms that grow inside bodies of water like your pool. Algae will often make your pool cloudy and greenish in colour. Algae can be thick and slimy and may appear to be green, black, or even yellow.
Algae is almost always the result of unbalanced pool water that has been still for an extended period of time. Since algae reproduces extremely quickly, it can take over your pool and clog your filters and pump in just a few weeks. This is why it is vital that algae be addressed and removed as soon as possible to prevent severe damage.
Can Algae Grow in a Closed Pool During Winter?
The short answer is that algae can definitely grow in a pool that has been closed for the winter. While the lack of sun and cold temperatures are not ideal for algae growth, they do not inhibit reproduction; they simply slow the growth.
If your pool water was not properly balanced before being closed, then algae spores can begin to reproduce even after the pool is covered. Additionally, if your pool was not adequately covered, then sunlight may be let into the water, allowing for photosynthesis. This is why it is so crucial that you book a professional pool opening and closing at the beginning and end of the season. This will help minimize the risk of algae growth during the off-season.
How to Prevent Algae Growth During Winter
Before you close your pool in the winter, you need to ensure that you apply the correct quantity of chemicals to the water. This involves adding a combination of sanitizer, balancers, and shock treatment. At Seaway Pools & Hot Tubs, we also stock algaecides in-store and online, which are specifically designed to oxidize algae growth.
However, it can be challenging for the average pool owner to precisely and accurately balance their pool with the right quantity of chemicals before winter. This is why it is highly recommended that you rely on a professional pool service provider for seasonal maintenance and for opening your swimming pool come spring.
Eliminate Algae in Your Swimming Pool with Seaway Pools & Hot Tubs
Algae growth in a closed pool is more common than many homeowners realize, especially when proper winterization steps are skipped. Taking the time to balance your water, use the right chemicals, and schedule professional maintenance can help prevent costly cleanups when spring arrives. If you open your pool and notice signs of algae, addressing it early can save both time and money. Contact Seaway Pools & Hot Tubs today for reliable pool and hot tub service.
