A swan is being treated after being shot in the head with a metal pellet at an “air gun hotspot” in March.
The stricken swan was rescued by the RSPCA after he was found by a passer-by with blood coming from the wound on Wednesday last week.
He was rushed to RSPCA East Winch Wildlife Centre, in Norfolk, for treatment and X-rays showed the metal pellet had lodged in his head.
Inspectors are now appealing for anyone who may have seen someone shooting an airgun on Coldham Bank in recent days to contact them.
Deputy chief inspector Jon Knight said an otter has been shot along this stretch of river.
He said: “This poor swan has suffered a traumatic injury and is not very well at all.
“This week we found 23 air gun gas cartridges in a five metre square area close to where the swan was found. The cartridges are of varying degrees of age, from rusty to new which suggests that perhaps one person or a group of people have been regularly actively shooting in the area for some time.
“People need to remember the devastating consequences that shooting at animals with air guns can have.
“In recent years I have been aware of several other shootings along this stretch of river, involving other swans, water birds and even an otter. It is quite a hotspot for these kind of attacks.
“It is very distressing to think that people take pleasure in causing such horrific injuries to defenceless animals. These are deliberate acts of cruelty and I would appeal to people’s consciences not to commit such an atrocious offence.
“This swan has suffered very serious injuries and it is not yet known whether he will survive.”