I think this is a juvenile eared Grebe. This is significant crop, probably smaller than 25% of full frame. I tried to get as much of the concentric rings of the water in the image to emphasize the setting. Lighting is a challenge as it comes in sideways.
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Technical Details
A7r4 Sony, ISO 640, 400 mm plus 2X, 2500th, F5 .6, handheld