When I approached the pond, even from a distance the turtles saw me and leaped into the water, or went into alert mode. They are amazingly fast when it comes to escape into water.
I moved slowly, and made myself comfortable on the grassy bank. Note to self: next time bring elbow cushioning materials. The grass and pebbles get a little uncomfortable after half an hour.
The turtles gradually returned. If I so much as moved my head suddenly, there was a general dive-and-submerge action. I practiced moving very slowly when resting my wrists, or not at all.