This is one of the classic Lake District walks, across the Wast Water screes, but it isn't for the faint of heart. The path across the screes runs across a steep slope all the way, and sometimes gets quite high above the lake. The scree slopes are sometimes unstable, and the path is sometimes blocked by recent falls. The middle section, made up of smaller stones, is probably worst while the south-western area is more of a boulder field and although it lacks a clear path tends to feel more stable. With this in mind the walk is still very worthwhile - crossing the screes is an experience and the walk back across Whin Rigg and Illgill Head offers some fantastic views back down to the lake and into the high fells.
Ascent: 2,350ft
Length: 8.5 miles
Map: OL 6 Lakes South-West
Last Walked: May 2013
We start from the National Trust Car Park just past the head of Wast Water.
The NT car park is on the side of the track that leads to Wasdale Head Hall Farm. Turn left out of the car park onto this track and follow it as it crosses Lingmell Gill. Turn right here to follow the track (now a permissive route) and follow it towards the lake. The track runs along the lake shore for a short distance then turns left to head towards the farm. At this point turn right onto a right of way.
This is the start of the screes path. We begin with a section that runs across increasingly steep grassy slopes. This soon brings us to the first of the scree slopes, a fairly stable affair at this point. The scree is broken into several sections, with the looser smaller stuff towards the middle and some grassy sections. The final section heading in this direction is made up of the larger boulders, so when you reach this section the worst is over. On occasions the path isn't passable - I've had to turn back once (see note below for alternative)
After the last section of boulders we reach another stretch of grassy slope, which brings us to the foot of the lake and eventually the start of the River Irt. We pass a small building, where the path becomes a good track. Just after the start of the river we reach a stone wall. A faint path runs uphill along this path - turn left and follow this path, with the wall to the right, as it climbs and then curves around to the right. This eventually brings us to the edge of Greathall Gill and another path that climbs up the fell. Turn left onto this path and follow it as it climbs rather steeply up towards the skyline. 
As we reach the top of the slope the path splits - either branch takes us to the ridge, but the right-hand branch runs around the top of the impressive ravine at the top of Greathall Gill while the left-hand branch cuts a bit of a corner. In either case our path brings us to a very clear path that runs along the ridge from Irton Pike on the right up to Whin Rigg and Illgill Head. Turn left onto this path.
Illgill Head comes into sight at the top of Whin Rigg. There are two paths across the intervening gap - one that runs along the grassy middle of the ridge and one that runs close to the top of the crags above the screes. I recommend the crag-top path, which never gets too close to the drop but does offer some fantastic views down towards the lake.
Illgill Head has two summits at the opposite ends of a short plateau. After the northern summit the path runs down toward a lower summit marked by a sizable cairn (this appears as a false summit when coming up from Wasdale Head). The path splits at this cairn - take the left-hand branch. This runs down the north-eastern corner of the fell, passes through a stone wall, then turns right to run down the left-hand side of the wall. 
At the base of this field we pass through another wall, cross Straighthead Gill and reach a well-constructed track. Follow this downhill past some ruined buildings and on past the Fell and Rock Climbing Club hut at Brackenclose. After passing the hut turn left onto the path that leads back towards the car park. Alternative Suggestion if Scree Path blocked
If the scree path is blocked I would suggest returning to the the Wasdale Head end and climbing Illgill Head. Look out for a right of way that leaves the track from Wasdale 
Hall Head Farm near the head of the lake. Follow this path through several fields until it reaches a track. Turn right onto this track and follow it as it climbs past Fence Wood. Stay on this track past some ruined buildings (ignoring the official right of way), and into a field. A clear path now runs up to the right of a stone wall (with Straighthead Gill on the other side). Follow this path until it reaches an area of craggy outcroppings (quite some way up). At this point two gates pass through the wall quite close to each other, leading onto a clear footpath. Follow this path to the summit (beware the false summits!). Return to Wasdale Head along the same path (after visiting Whin Rigg if you wish).