Pond ice must be over 4 inches thick (10 cms) to support walking, skating etc. if it is clear ice. White ice (with snow/air) is weaker even at 4 inches.
A regular brick thickness is 3 5/8” (9 cms) if you want to compare.
Pond edge ice forms first because it's still, shallow, and exposed, but it's often weaker and more dangerous than thicker, clearer ice in the center, especially near inlets/outlets where water flows.
Thetis Island Vol. Fire Dept.