Westgate Park has had a checkered history.
It started as a salt marsh that extended all the way up river to Flemington. Sand mining started in the 1930's, and continued for a decade. Part of the excavated land was filled with water forming the southern lake.The remainder of the park became a rubbish tip (for the next 23 years).
During World War II an aircraft factory and airfield occupied the site.
The present day park is a 54 hectare wetlands that was developed in 1984 as part of the Victorian 150th anniversary celebrations.
It is the breeding grounds of the Australia (not so) White Ibis.
However, the cache location has more to do with the bridge than with flora or fauna characteristics of the park.
Although I'm sure you will say hello to a few spiders in your search.