Citadel Estates wants to convert and extend the former Tarn End House Hotel at Talkin Tarn near Brampton.
The Save Talkin Tarn group, created on social networking site Facebook, said the plans would “ruin” the area.
The developer said the scheme was in the public interest as a new boat house for a local rowing club would be built.
Alan Sykes, who created the Facebook group, said the plans would “destroy” the area’s beauty and ambiance.
He said: “It is essentially planting a small village in open countryside.
“This is 15 houses on less than half an acre of land in the middle of a beauty spot and it is bound to cause disruption and disturbance to an otherwise lovely and tranquil place.”
The site, which overlooks the Talkin Tarn country park, was been sold to the developer by Carlisle City Council for £450,000 earlier this year.
The plans are expected to go before the council’s planning committee on 2 October.
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