Water snake with a yellow criss-cross on a black background?

I saw a 60 cm long, very skinny (~15 mm diameter), black with yellow diagonal criss-cross patterned snake swimming in a pond this afternoon in northern Taiwan.

It was swimming near the top of the water and I could see it very clearly, but as soon as it noticed me it dropped most of its body to the bottom of this shallow pond and just kept part of its head above water, so the photos are not very clear.

I tried to wait for it to continue but something else disturbed it and it took off.

Is it possible to identify this snake or at least narrow down the options?

First image is cropped from the large image. I have played with contrast, color and sharpness to make the pattern and color look most like what I remember before it dropped its body lower into the murky water.

sketch of pattern as I remember it