NOT frogspawn - what is it?

Attached to some LONG strands of blanketweed I found several strings of ??
eggs ?? - but what are they ?

Definately not frogspawn. These are jelly strings, between 4 and 7 inches
long, with black spots all in a line, about 20 eggs per string.

I'm in UK. Pond contains a few brand-new young Koi, about 3", a couple of
Koi introduced last year (now about 4" long, and an old Koi (10 years), and
possibly bream (they bred in the pond some years ago, just once - never did
see their eggs - since which a heron ate just about everything. Whether they
are still there, impossible to say - hard to see at best of times!.

We have the inevitable frogs, and I've seen both the odd toad and newt under
the rockery stones - very shy creatures they are too! However, never seen
toads or newts in the pond.

Any idea what these egg strings could be, please?