The 125-year lease to the estate around the beauty spot is being sold in four lots by owners Severn Trent in an £11 million land deal.
United Utilities was named as Severn Trent's preferred bidder for two of the lots.
But the firm has revealed the deal is unlikely to go ahead because it actually wanted to buy the whole estate.
A company spokesman said: "United Utilities bid for the leasehold of the Lake Vyrnwy estate in order to replicate at the reservoir and surrounding land its environmental catchment programme that improves water quality and protects ecosystems.
"However, it has become clear through the sale process that more certainty is needed around the ownership of the different lots for sale to enable that programme to be implemented.
"United Utilities has contacted Severn Trent Water to express an interest in the purchase of the freehold of the whole estate but Severn Trent Water has rejected that offer.
"United Utilities remains committed to the future of the Lake Vyrnwy estate and will continue to have a presence there as the lake provides water to the people of Cheshire and Merseyside.
"Unfortunately, as things currently stand, it doesn't appear that it will be as the estate's owner."
The lease of the 23,000-acre estate was put up for sale in 2010 by owners Severn Trent, in what was described as the largest land sale in the UK in living memory.
The £11 million sale included agriculture, forestry and commercial property around the lake – but not the lake itself.
United Utilities, in partnership with the RSPB, was named in 2011 as the preferred bidder for large parts of the agricultural land. Severn Trent has confirmed its preferred bidder had withdrawn.