A closed season is where anglers are not allowed to catch fish in rivers. The Environment Agency in Britain says that the benefit of this is not only to prevent hard to breeding fish, but also to prevent other harm that anglers cause:
"It is recommended that closed seasons are imposed where any wildlife, such as breeding fish, amphibians and birds, will benefit from not being disturbed as much."
"Wintering wildfowl flocks also benefit from less disturbance, especially at main sites where there are large numbers of birds. A closed season may also allow vegetation on the bankside to recover."