A barn owl has been shot and otters found dead at a reserve in recent months, according to wildlife officers.
Herefordshire Wildlife Trust says it is "alarmed" by incidents near Bodenham Lake Nature Reserve.
At the end of January, the owl was found dead at the lake shore, while two otters were killed in suspicious circumstances in November.
There are also reports of invasive species of crayfish being moved into new waters, threatening native animals.
The trust says the death of the barn owl is particularly concerning as the birds are in decline across the UK.
The death of the otters just south of the lake, near Wellington, follows reports of illegal trapping of the animals in the nearby area.
Otters have the highest level of legal protection in the UK, after the animals were driven to near extinction in much of the country in the mid-20th century.
Sophie Cowling, from the trust, said it is waiting on results of a post mortem into the deaths from Cardiff University.
American signal crayfish are also being taken from the River Lugg at Bodenham to other watercourses in Herefordshire which the trust says poses a threat to native white clawed crayfish,
The American species often carries crayfish plague, an infection deadly to native species which are also at risk of extinction.
The trust is calling for anyone with information about any of the recent crimes to contact them or West Mercia Police.