Here's a rough calculation of the crowd size.

Using Google maps, an approximation of distances is possible, for example the bridge over the street is about 120 feet long.

The area marked by the purple lines calculates to 17,100 sq feet.

From a Wired article about estimating crowd sizes,

"In a loose crowd, where people are at an arms length of each other, figure about 10 square feet of space per person.

In a tighter crowd, it's about half that, or 5 square feet.

In a packed crowd, it's more like 2.5 square feet."

If the 5 square feet per person number is used, it gives 3420 people.

Because the crowd on the left side and at the edges is spread out a lot more and the seated take up more room, I would say that the total number is closer to 3000 but definitely not more than 3500.