The answer to 'why is my drainage system invasive plants' is that invasive plants can often take root in and clog drainage systems. This can happen when seeds or plant fragments get carried into the drainage system, either through water flow or by animals. As the plants grow, they can obstruct the flow of water and cause backups or flooding.
Some common symptoms of invasive plants in a drainage system include slow or standing water, visible plant growth in the drains, and water pooling around the drainage outlets. To address this issue, you'll need to clear out the invasive plants and take steps to prevent them from returning, such as regularly inspecting and maintaining the drainage system.