I want to build a bridge over the narrow section of my pond. Comparing lumber, I found the cost differences between pine, spruce, cedar, redwood and pressure-treated wood to be really large. Cedar and redwood are the most expensive, whereas pine and spruce are the cheapest. I don’t want my bridge to rot in our wet weather, so I was thinking about pressure-treated wood. Is there a problem using this for my pond bridge?
Due to environmental concerns about arsenic leaching into soil and water, arsenic-based pressure-treated lumber is being phased out. You can still buy it, however. On one hand, I know of no reliable studies showing that the amounts of arsenic that could potentially leach out of a small bridge would harm the fish, plants or other animals around your pond; on the other hand, I know of no studies that say it won’t.
Err on the side of caution and go with one of the other materials: cedar or redwood. Both will hold up nicely in the weather and last decades, if properly maintained. Given their longevity, I do not think the cost is prohibitive.
You can certainly make the bridge out of a softwood, such as pine or spruce, and that would be the least expensive. However, the wood would have to be sealed with a paint or stain, and recoated every couple of years. Even then, it might have to be replaced every eight to 10 years. That is why I think cedar or redwood is the real bargain. If you go the softwood route, don’t paint or stain the bridge while it is over pond water. You will have to move it away, so spills and drips cannot get into the pond.