Is there an issue with the new strap for the 310xt while swimming (i.e., is it not waterproof)?
One or 2 folk have reported a problem with the watch strap coming adrift in the swim. Looks like there may be some defective straps around. In terms of waterproofness, there are no problems.
Maybe check the security of your watch strap by giving the 310 a good pull might be worth doing before getting into a mass swim start.
The new HR strap is deemed waterproof and we’ve not experienced any problems to date. But we never had any issues with the 305 HR strap in the water anyway.