Bricks are generally safe and useful to install anywhere around the edges of a pond. Putting them in the water is a different question that depends on the exact type of brick you’re considering. Regular red bricks are perfectly safe to use inside of a pond, but they may not hold up in a cold climate as the water in the clay freezes and breaks the brick apart. Engineering bricks look like the same product, but they’re dried at a higher temperature that makes the brick tougher and more resistant to damage over time. This will give you the look of red or gray brick with the long lasting cover you need to keep your liners held in place.
Concrete bricks, blocks, and pavers are also generally safe to add to a pond. If you have fish and are concerned about sudden changes in pH, let any new concrete bricks you want to add rest outdoors away from the pond for a few months. This exposure to the sun, wind, and rain ages the material so it doesn’t affect the pH of the water. Any older concrete blocks that have already sat out around the edges of the pond or anywhere else are likely safe to use in a pond as is, as long as there’s no stain, paint, or other residue on them.
