The idea that otters frequently swim in lines has not been popular with cryptozoologists as this post shows.
There has been otters sighted at the lake:
"just a few mounths ago there was a report of a otter in there so it was probelt the same one there" callum semmens 14, Neath
There has been a ongoing resurgence in otter numbers over the last ten years in the Swansea area as across the UK. Anglers on the Tawe are blaming otters for fish losses. See the Otter Survey of Wales 2002 which reports
In the 1977/8 and 1984/5 surveys, all the sites in this
hydrometric area were negative but a major increase
was evident in 1991 with 44% of sites positive. A
further 17 positive sites in 2002 now brings the
proportion of positive sites to 78% (81% if only the
sites common to all surveys are compared).
The greatest increases were associated with the
upper reaches of the Tawe and tributaries such as the
Twrch and Lower Clydach, where all the previously
negative sites became positive. Smaller rivers flowing
into the Loughor estuary also showed increases. Also
significant is the presence of otters on the Lliedi
reservoirs, near Llanelli, in an area with considerable
Otters are mainly found upstream then but the closeness of Pluck lake to the river means that reports of otters here are not impossible. Perhaps most intriguing is the mystery plague of deaths blamed on otters or mink in Swansea a few years ago which caused panic amongst pond owners.
News - South West Wales - 'Mink' warning after fish deaths
Since the late summer, an unknown animal has been preying on ponds in back gardens across the Killay and Derwen Fawr areas, killing dozens of fish.
Members of a gardening club believe a mink or possibly an otter is responsible and are urging people to protect their ponds.
Following an attack that left around a dozen of their neighbour's Koi carp decapitated, Alma and Ray Jenkins have covered the pond at their home on Dylan Road in Killay with mesh.
There was blood and fish remains everywhere but just the heads were takenAlma Jenkins
The couple say they know of at least eight incidents in the area in the past six months, but believe there could be many more that have gone unreported.
There are other reports:
RW SwanseaThe problem for saying the Pluck Lake sighting was an otter is the distance. Steve Jenkins was only 3-4m from the creature. Thus it cannot be an otter I think.
At 4.00am on 20th May I saw an adult otter on the Oystermouth Road directly opposite tescos and swansea i was driving at the time and got within 20 feet of it and saw it for at least 30 seconds i was struck at how big it was and obviously that it was so close to the city centre. I didnt think that there was a wild population in swansea and actually reported it to the police.