Dear Beloved Monster - S1.E14

Professor Jonathan Slater's experiments with DNA go awry when he accidentally creates a hideous reptile-like creature. The monster escapes the lab and claims several victims as it takes refuge in a nearby lake. After the deaths, the professor resolves to kills the creature himself. The poison he pours into the water only briefly knocks the monster out. Once it reawakens, Professor Slater realizes he can't bear to destroy his creation.