He sent me some history of the track which he has kindly allowed me to quote here:
"Hi Rob,
I used to race on Thursdays at 6.30pm in what was known as Westgate Dirt Crits. I'd say I raced down there regularly from 2011 to 2013. I know before my time they used to race on the north side of the bridge on the hills around the lakes. In my time down there racing was largely restricted to the south side of the bridge along the strip from the river on the western edge to where the shipping container and the remnants of the pump track are to the east. This shows the typical loop that I recall very well: https://www.youtube.com/watch?v=J-r0MDll2-A
The bridge strengthening works and the new Melbourne Water odour control plant chipped away at the track and it was always being adjusted. There was an accident where a rider hit a pedestrian at one stage and the course was cropped further to stay south of the shared path. The final straw was the Webb Dock redevelopment which ate into the southern boundary and cleared much of the single-track that the MTB used to follow. I've not been down there for a while but I can see on aerial pics that there is not much left. I know the MTB riders were in touch with the Council and the Friends of Westgate Park. The works and a dwindling lack of interest from riders meant that there hasn't been racing there for at least 2 years I'd say."
There is certainly not much left in the way of tracks, but it is worth having a look around in this corner of the park.