There are several canal systems in Wales, the four main systems being the Llangollen Canal, the Monmouthshire and Brecon Canal, the Montgomery Canal and the Swansea Canal. All of the Welsh canals were created during the Industrial Revolution for transporting materials to and from industrial centres and ports. While many canal sections are still navigable, others are not and these can be both of international, national and local biodiversity importance, primarily for aquatic plants and invertebrates, e.g., dragonflies and damselflies. However, the biodiversity of the canals is linked inextricably to their management – and especially the management of the stretches that are not currently navigable. The three main reference states for canals are outlined briefly below. As a general rule, it is the balance of these reference states that is important with, at any given time, at least 75% of the disused stretches of canal having at least some open water visible, with most stretches having 50-80% open water.