The third reference state for canals is a mature successional phase of development associated with disused stretches of canal. These mature stretches tend to be dominated by emergent species such as bur-reed (Sparganium erectum), bulrush (Typha latifolia) and common reed (Phragmites australis). In these stretches the channel of open water is narrowing and the emergent vegetation is limiting the amount of light that can penetrate the water for the submerged aquatic plants. This is a recognised phase of development and can support good dragonfly and damselfly populations, but left unmanaged, the emergent vegetation will eventually close up at the expense of the open water. As the stretches of canal reach this phase of development they become priorities for weed cutting and dredging.