A black-and-white cat was found drowned in the Redwood Shores lagoon on Wednesday with a 5-pound dumbbell tied around its neck.
The male cat was discovered by Redwood City public works employees and brought to the Peninsula Humane Society, shelter spokesman Scott Delucchi said.
The dumbbell was attached to the cat's neck with zip ties, he said.
A PHS veterinarian determined that the cat was about 12 years old and was in the water for two to three days.
The cat's front paws were declawed, indicating that he was likely someone's pet, Delucchi said.
"We believe this was an owned cat and that someone intentionally killed him in a horrific way," he said.
The nature of the crime indicates clear intent to harm the animal, which is a felony, he said.
The PHS was initially offering a $1,000 reward to help find the person responsible for the crime.
A resident who learned of the incident pledged to give an additional $250 to the reward this morning and the owner of the Swingin' Door Pub in San Mateo offered an additional $1,000, bringing the reward to $2,250.
Delucchi said the PHS has been looking through reports of lost cats and checking Craiglist for leads, but nothing has come up yet.
The cat did not have a collar or an identification microchip.
Anyone with information about the crime is urged to call the Peninsula Humane Society at (650) 340-8200 or email at firstname.lastname@example.org.