VictorIE
Hi,

Apologies, this is an old note.

In the 19th and 20th centuries, Belfast had a large number of mill ponds (for motive power) and small reservoirs (for drinking water and industrial uses). Some remain, but are mostly used for recreation.

Near your note marker, I can immediately find three:
https://www.openstreetmap.org/way/38309598/
https://www.openstreetmap.org/way/926877993/
https://www.openstreetmap.org/way/38622239/

If you look at the "Ireland British War Office 1:25k GSGS 3906" image set for here https://www.openstreetmap.org/edit?note=1161633#map=17/54.628750/-5.984914 then you can find more For Belfast, the old map seems to date from about 1900.

Open Infrastructure Map https://openinframap.org/#9.29/54.5952/-6.0433/A,B,L,W highlights some of the remaining ones.