Low water levels at Longue Hougue expose gravestones that fell during a landslip in 1969.
Longue Hougue used to be a quarry and in 1969 there was a rock fall.
This caused a number of graves from the nearby St Sampsons churchyard to fall part way down the rock face.
The quarry is now a reservoir and unusually low water levels have exposed a rock-shelf and some dressed granite gravestones.
As human remains may also be visible, the police have to ensure that they date back to the landslide, so they are investigating.
Guernsey Water says that a visual survey will take place today (14 November) to check whether or not there has been a recent land slip, and to see if any further action is needed.
The company says it's helping the police with their investigation and it's been in touch with the Dean of Guernsey and the St Sampson’s Parish Cemetery Committee.

Guernsey castle to host 150 performers
Trial of man accused of Sarah Groves' murder could resume
Corridor gallery opens in Guernsey hospital
Guernsey Prison Governor to 'step aside' during conduct investigation
Guernsey reservoir walk reopens following 'extensive' tree surgery
Two more Asian Hornets found in the Bailiwick of Guernsey
Guernsey Autism charity gets States commissioning deal
Digital travel permissions extended to Channel Islands this month