Emma, too late if you've gone this weekend, but for future reference for you or anybody:
Chelmarsh Scrape in spr/sum is good for close views of Reed buntings, Sedge/Reed Warblers, Com Whitethroat, Cuckoos and sometimes Hobby (check the two dead trees at the far end of the scrape). LRP try to breed but aren't usually successful, Oystercatchers and Lapwing generally try too. Green Sandpipers arrive now and stay for the rest of the year and other Sandpiper species pass through. The Reservoir has many GC Grebes, Herons etc. Sometimes Terns are around and if you're really lucky you may even see an Osprey, but don't hold your breath on that one!
In autumn/winter the Scrape hide is very good for seeing Water Rail (leave the door open and keep your eye on the little wet area by the door - great views!) and quite a few Jack Snipe winter there and sometimes show. Various waders turn up briefly on passage and Lapwing and Teal increase in numbers. The reservoir has a very large gull roost in winter and rarities are sometimes found. Divers and Scoters have also been present.
The reserve parking area is half a mile off the B4555. Three miles out of Bridgnorth, on the bend just after the Chelmarsh sign, there is large sign for 'Dinney Barns'. Turn up here and follow road as it bends to the right towards the farm. Keep going straight on, down a short hill and the car park is at the bottom. This is at the end of the causeway from which you can look over the reservoir. The metal gate in the car park leads to the Scrape hide. There is another hide at the far end of the scrape which isn't usually used as walking to it can scare all the birds off the scrape! Though with the hedge in leaf in summer it should be ok!
Hares and Green Woodpeckers are also near the farm and car park. If you park in the village as 'upstarts' mentioned earlier, look out for Spotted Flys which nest every year in the wysteria on the house next to the church.
I would say May and a winter month are the best times to visit.
Hope this helps
(it's in Shropshire btw)