This is a very good read for Rush Lake trek general information:
Flickr: Discussing Rush Lake and Rush Peak Trek Information in The Trekkerz
I haven't heard of trek from Hispar side but if there is a trek then it would be one hell of a tough one. So avoid this idea
On Barpu side, there are 3 possible itineraries to reach Rush Lake:
2 days trek:
- Hopar to Baricho Kor
- Baricho Kor - Rush Lake
3 days trek:
- Hopar to Barpu Giram
- Barpu Giram to Gurenz / Gutenz
- Gurenz / Gutenz to Rush Lake
4 days trek
- Hopar to Shishkin
- Shishkin to Barpu Giram
- Barpu Giram to Gurenz
- Gurenz to Rush Lake
Now coming back has also many possibilities. Either follow one of the above treks to use same route or change your route as follows:
Option 1
- Rush Lake - Phai Pheri
- Phai Pheri - Hamdar
- Hamdar to Hopar
Option 2
- Rush Lake - Miar
- Miar to Hamdar / Hapakund
- Hamdar / Hapakund to Hopar
You can also go all the way to Hopar on day 2 here
Sequence of different destinations on Rush Lake trek
1- Hopar - Shishkin: Need to cross Hopar glacier (aka Bualtar)
2- Shishkin - Barpu Giram: Need to cross Barpu glacier
3- Barpu Giram - Baricho Kor: Walk continues on left side of Barpu glacier and you reach this green pasture and camping site near trees
4- Baricho Kor - Gutenz and Chedan Hirai: From Baricho Kor steep climb starts over rocks and then gradual grassy/rocky incline starts which passes through Gutenz and Chedan Hirai
5- Gutenz and Chedan Hirai - Rush Lake: Not a tough trek and gradual climb
Note that route also climbs up from Barpu Giram to upper ridges.
On return
1- Rush Lake - Phai Pheri: If u r coming from Hopar then this point is ahead of Baricho Kor from where climb starts. So, if u plan to change route on return then drop down to this location.
2- Phai Pheri - Miar: Cross the junction of Barpu and Summayar glaciers and first point across Barpu glacier is Miar
3- Miar - Hamdar - Hapakund - Shishkin - Hopar: Now keep walking on other side of Barpu glacier and these points will come one after the other. At the end, u need to cross again Hopar glaicer to complete the trek.
Here is the map to give you idea of different locations. These are not exact as i have not done this trek personally
I have no idea of descend route from Rusk Lake to Phai Pheri so just marked the route.
Rush Lake Trek Map by Mobeen Mazhar, on Flickr