 The estuary has a maximum width of , and its depth ranges from .Tides are semi-diurnal, ranging from ; their upriver propagation is limited by falls situated from the mouth at Moinho dos Canais.In the lower estuary there are nature reserves covering a total of ; in Spain, the Marismas de Isla Cristina and, in Portugal, the Reserva Natural do Sapal de Castro Marim e Vila Real de Santo António (English