In recent years, it housed over 55,000 migrating birds, including Saunders's gull (Chroicocephalus saundersi) and a quarter of the world's Black-faced spoonbill (Platalea minor) population.

The reserve also includes inter-tidal mangroves along with 24 traditionally operated shrimp ponds (called Gei Wai locally) to provide food for the birds.

Small Asian mongooses are quite common in the reserve, often encountered by visitors near Gei Wai ponds during the day in winter.

The marshes also have rich insect biodiversity, housing the endemic Mai Po bent-winged firefly (Pteroptyx maipo) was discovered.

To understand the seasonal population changes, distribution and habitat requirements of the species, WWF Hong Kong have been carrying out firefly surveys of the nature reserve.

[7] In February 2008, the Hong Kong government closed Mai Po for 21 days following the discovery of a great egret infected with H5N1, also known as avian flu.