The Olympic and Paralympic sailing events will be hosted at the Weymouth and Portland National Sailing Academy. Contractors Dean and Dyball started in March to enhance the existing sailing facilities with a permanent 250m slipway and race-boat parking, lifting and mooring facilities.
Construction has passed the halfway stage, with 70,000 tons of Portland stone used to reclaim 18,000 sq m of land in front of the sailing academy to form the new slipway.
There is a 200m breakwater to protect the facilities, and a pier is being constructed featuring two yacht lifting cranes and a pontoon with 70 berths for race-boats.
Work is expected to be finished in November making it the first venue to be ready for the 2012 Games.
Chairman of the London 2012 organising committee Sebastian Coe said: "The success of our sailors was one of the highlights of a fantastic Beijing Games for Team GB so I'm delighted that we're on track to deliver enhanced sailing facilities at Weymouth and Portland for our sailors to train well ahead of 2012.
"Our plans are driven by legacy and these enhanced facilities will also provide new opportunities and facilities for people from a wide range of backgrounds and abilities to experience the thrill of sailing for many years to come."
ODA chief executive David Higgins added: "Weymouth and Portland was the first venue for 2012 to start construction work so reaching the final stages of the project is another important milestone.
"The huge progress we're making at Weymouth and Portland means we're on course to finish work ahead of schedule, helping us deliver an early legacy of world-class facilities for elite athletes and the local community to use well ahead of 2012."