Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 446.14
Broken: version: 2.83.0, branch: master, commit date: 2020-06-03 14:38, hash: rB211b6c29f771
Short description of error
Strange artefacts are being created by the denoiser, firefly like bright and dark pixels where there were no such artefacts in the 'Noisy Image'. Looking into the 'Denoising Depth' pass reveals negated depth values around the artefacts. In the supplied .blend it seems to be caused by some weird interaction between the sun lamp and the water material with a black diffuse.
(White values are ~90 black are ~-90)
Exact steps for others to reproduce the error
Render frames from supplied .blend