Celestine Pool is, tragically, one of the hot springs that has claimed a human life. As in many of the pools around Yellowstone, the water in this pretty pool is usually within a few degrees of boiling. There is little hope of surviving a fall into such a pool.
As far as geyser activity is concerned, Celestine is a frequent but modest performer. Boiling eruptions to a height of about 4 feet, occasionally slightly more according to some 2015 reports, are "frequent" (Bryan) and last for a few minutes at a time. Bryan also notes that there appear to be connections between its activity and that of Silex Spring. No eruptions of the latter have been recorded in the last few years, but Celestine was certainly active in 2015 and probably 2016 as well.