Timber Falls (2007) on Netflix

Plot summary

Mike and Sheryl set out from Virginia for a weekend of hiking and camping at Lake Kimbrabow State Park, in West Virginia. At the park, a ranger points them to one of two trails, and while they hesitate a woman they meet, Ida, recommends Timber Falls and they choose it. Out in the woods, three local hunters offer the couple a jar of their own alcohol, and Sheryl talks Mike into dumping the ammunition for his revolver. They pitch their tent beside a lake and spend the night there, watched from outside by a figure neither of them sees. The next morning Sheryl goes into the water to bathe, and when Mike wakes she is gone. Only her necklace is left at the lake, and he begins to search for her.