An entire Llanelli river appears to have been swallowed up by sinkhole.
Natural Resources Wales are investigating after the entire water flow of the Afon Lliedi under a bridge in the Llanerch area of the town disappeared on Monday (August 16).
Around 50 dead fish have been seen in the vicinity of the hole.
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Officers say the situation is under control and safety measures have been put in place to protect staff responding to the incident and the public.
Carmarthenshire County Council has closed the bridge as a precaution due to concerns about its stability.
NRW’s integrated workforce was sent to the area and has installed a pump to take water around the hole and back into the river channel downstream of the hole.
Ioan Williams, duty tactical manager for south west Wales said: "We are working closely with our Carmarthenshire County Council colleagues to understand what is happening and to put safety provisions in place.
"We can confirm that approximately 50 dead fish have been seen in the immediate area. Living fish have been seen in small pools in the river channel down river.
"We hope that pumping the river flow beyond the hole will reduce the number of fish killed by providing some river flow to the fish trapped in small pools."
There is no obvious reappearance of the water and the direction of the water flow into the hole is unknown. The Coal Authority is attending on Tuesday to assess the situation further.
NRW is urging anyone who spots something which may be connected to the incident to call their incident line on 0300 065 3000.
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