Swiss assisted suicide clinic Dignitas has been accused of dumping dozens of urns filled with human remains in a nearby lake
Divers said they lost count of the number of containers full of ashes they had retrieved from the bed of nearby Lake Zurich.
Each apparently bore the name of the controversial clinic on its side.
Roman Ruetz, who made the discovery, said: "We stopped counting at 50 urns. They're all lying on a heap."
Dignitas founder Ludwig A Minelli, who has refused to comment on the allegations, could be jailed if the matter goes to court.
Judges can imprison organisers of unauthorised lake burials for three years, and dish out a fine of around £32,000.
The clinic has been accused of unlawfully depositing human remains before.
Swiss authorities began a probe in October 2008 after two Dignitas members were seen tipping the ashes of 20 people into Lake Zurich.
At the same time, the clinic was warned by waste disposal officials after hundreds of small human bone fragments washed up on the shore of the beauty spot.