Grebe nest gets abandoned!!!

Last Sunday I kayaked and as I left, the Grebes were using there nest as normal incubating there 4 eggs but after Monday things were very different with the pair.
On Tuesday we noticed the Grebes staying away from there nest and after hearing about some young fisherman in 3 kayaks near the nest I was very worried and without being able to check the nest for the eggs I could not figure out why they had left the nest as when I kayak past they always return to the nest.
They both seemed relaxed and were happy to pose for the camera

So was it Flash getting aggressive with the Grebes making them change there mind as there young would be in danger from Flash as his aggression is increasing towards all the water birds on the lake or was it human interference or even possibly Otter or mink but my theory is a mix of 2 of my ideas.
Later in the week I found more predated nests and I found a few clues in the area at the weekend that may reveal what the Grebe egg thief was.

Thanks for reading

Mike