Koo-wee-rup: The remains of the old loco area (turntable pit, inspection pit) exist on the down side of the level crossing. The formation towards Bayles can be see curving away.
From Koo-wee-rup to Heath Hill, the line ran across the reclaimed Koo-wee-rup swamp, and is this is all but dead flat, there is next to nothing in the way of earthworks to see.
Bayles: The station yard is now a fauna sanctuary and there is a $2(?) admission, and probably not much (of railway interest) to see, although I haven't looked. There is a sign, a station nameboard, a (road) weighbridge, and maybe a mile post.
From Bayles to Catani the line ran on the north side of the canal. You can see the alignment readily enough, but that is about all.
A road has been built on the formation through Catani station. A few trees on an uncharacteristic mound mark the remains of the platform.
A road continues on the formation most of the way to Yannathan.
Yannathan station ground can be discerned by the fences marking the boundary if you know where to look.
I haven't inspected the route from Yannathan to Heath Hill as it is not very accessible.
There are buildings in the former Heath Hill station grounds. I believe that one may be the old D.R.
From Heath Hill to Triholm the line followed the Lang Lang River, so some earthworks are visible.
Just beyond Heath Hill the remains of a large cutting exist. The road used to cross this on a bridge, but the cutting is now filled in at this point.
From about a mile beyond Heath Hill to Athlone a road parallels or is built on the formation, including through a curved cutting of reasonable size. There are remains of a couple of bridges in this section.
At Topiram the cattle yards remain.
At Athlone and Triholm there are signs commemorating the line. The formation where the line crosses the (current) road is easily visible.
From Triholm to Strezlecki the line climbed at 1 in 30 to 1 in 40, and earthworks were extensive. However, apart from a short distance part Triholm and a short distance before Strezlecki, most of this is well away from the nearest road and not readily visible. (Although I think somebody on aus.rail did say that it could be seen from the road that runs along the other side of the valley.)
Just before Strezlecki there is the site of a very large trestle, followed by a very deep cutting which was previously crossed by a road bridge. Part of this cutting has been filled by using it as a tip, but enough remains to appreciate it.
From here to Strezlecki the line paralleled the main road and is mostly easily seen. There is a metal shed on the station grounds, and the formation continues some distance past the station to the turntable site cut into the side of the hill. It must have had the best view of any turntable in the state! Unfortunately, this last section from Triholm was only open for eight years, if I recall correctly.
To find the turntable site (pit and concrete abutments exist), you have to travel down a gravel road with a name that has something to do with a dog. You should know what I mean when you see it! [On aus.rail someone did supply the name of this road, but again I forget what it was. I will change this if I remember or someone else reminds me.]