The Pumping Station is an area in the watery section of The Slums. It is one of the only places with virtually no city walls whatsoever (for example, even Dead Town has walls as a barricade). However, it does have a little robot underneath the water that will come out and shoot anyone who strays too far from the station and beach itself.
 Jak II
It seems that the environment changes every single time that a new mission is accepted. The entire level is accessible throughout the entire game (excluding the section leading to The Dig), but some of the Pumping Station's machinery is turned off when you are not on a mission that uses that machinery.
In the first mission that Jak and Daxter take from The Underground into the Pumping Station involves them turning the water back on for the city that the Baron had shut off. During this mission, the area is loaded with Hoppers and Frog-Lizards. It is also the first mission that Precursor Orbs can be obtained in after first stepping into Haven City (that is required). There are various elevators and other such pieces of machinery that are running, but not much else. There are a few cliffs that can be used to travel between the different sections.
The next mission that the team takes is given to them by Krew and Sig. They must travel with Sig in order to "bag some trophies" for the Hip Hop Saloon. These trophies are in the form of Metal Juicers, which appear all over the place on various cliffs. There is now destroyed rubble, thanks to Sig's Peace Maker. However, there are also turning pieces of machinery that are used to climb up, onto a different section. Jak must use a jump-punch on the tables that are up in the air to drop them in order to get Sig across. They stay this way.
Afterwards, the group takes a mission (once again from The Underground) to go assist one of Torn's Krimzon Guard friends. This time, there is much more machinery, and there are crates loaded with Blaster ammo, like the second time this area was visited. There are more running elevators that must be used, and there are more pieces of machinery. Jak also finds out that this used to be a main area for Mar, as there is the Seal of Mar on a rock that the Krimzon Guards are searching for. There also seem to be more Metal Heads here during this mission.
The Pumping Station connects directly to The Dig via a rail. It can only be accessed after Jak has obtained the JET-Board for free use across Haven City, aid is used whenever the Transport Zoomer is not sitting at the Port.
The enemies found in the Pumping Station also change during the missions. For example, the first mission is filled with things like Hoppers and Frog-Lizards. However, the other missions are filled with more vicious creatures, such as the Metal Heads. There is also a Waterbot that will shoot anyone who trespasses too far out away from the beach.
There are no residents of the Pumping Station. However, Ashelin and Sig are both found in this area during missions. It is assumed that the Krimzon Guard does come here every now and then because of the connection to The Dig, where they use a Transport Zoomer. However, as there are no city walls, nobody is allowed to live here.