On Crystal Isles, at about 42 40 there is a little white lake. There is a waterfall in the lake, and on either sides close to the waterfall are around 1000 silica pearls, + the ones in the beaver dams. Just be careful because in my case there was a Yuty pretty close by.
Anglers are the best at harvesting these, tame a high lvl with good weight, good weight from my experience is around 700+ the one I got on my sever was a 250 tame and had 763 base after tame, if you can’t get one just run around the beaches and collect them. I got 5.8k with my angler is less then 5 min, I play with 2x harvesting on mobile by the way