The following sites are also good birding spots around Newark:
Langford Lowfields is an RSPB reserve in the making, a few miles north of Newark. Although still a sand and gravel quarry being worked by Tarmac, it is being progressively restored to reedbed - and reedbed on a large scale. Unfortunately the first phase, which had been successfully restored to reedbed, had to be reprofiled, but I understand that its replacement will be even better.
Already, this site has hosted booming Bittern (although breeding has yet to occur) and nesting Marsh Harrier. Cetti's Warbler is now resident, Avocet have bred, and Bearded Tits have been recorded (but have yet to take up residence) - it's like a little bit of East Anglia, in the Midlands! It has also attracted a few rarities - in 2009, the county's first Glossy Ibis for a hundred years put in a brief appearance, whilst Purple Heron, Great White Egret and Common Crane have also been seen recently, along with Red-necked Phalarope.
The site can be accessed from a number of points, but easiest is the new carpark accessed off Cottage Lane, at the far southern end of Collingham village (accessed off the A1133 just north of the railway crossing). For more details about the reserve, including a blog and recent sightings, check out the Langford Lowfields webpage.
Kilvington Lakes is an area of restored gypsum workings next to the village of Alverton. There is a small viewing point (with a sightings board) overlooking the West Lake, accessed off the road just south of the bridge over the disused railway line. The East and North Lakes can be partially seen from the viewing point; the East Lake can also be seen from the roadway where the former quarry office used to be. The site has produced an excellent selection of birds in recent years, including Great Northern Diver, Green-winged Teal, Pectoral Sandpiper, Purple Sandpiper, Red-necked Phalarope and Montagu's Harrier.
Spalford Warren is a Notts Wildlife Trust reserve and SSSI next to the A1133 between Besthorpe and Spalford villages. The Trust have done a lot of work recently to remove coniferous trees and restore acid grassland and heathland. Woodlark breed. See the NWT website for more details.
Besthorpe Warren is another SSSI, just to the north-east of Besthorpe Village. The birding is a bit limited, but it is a good bet for Woodcock in the winter.