First, I am no expert on this topic, I am simply synthesizing several different sources of information along with the very good work of others. Since the "thing" featured in this question has appeared elsewhere, it deserves an answer.
These appear to be eggs of Chironomous midges (wikipedia). This conclusion is based largely on reading the three-part blog by Tom of askanaturalist.com
Part 1, Part 2, Part 3 which is very thorough. In the last part of that blog, it is stated "chironomid eggs are nearly always elongated or oval shaped. Caddisfly eggs, on the other hand, are nearly always spherical." Looking at the pictures here and on the other SO questions (here and here) it appears that the eggs are indeed elongated rather than spherical. Hence they are apparently Chironomous midge eggs.