One news story across six platforms: the Cwmderwen flood

Item	Who made it? Can I check them?	Evidence it gives	Does another item agree?	/5	Reason for my score
A: citizen video	Siân Pritchard, a named local walking group leader. On the app since 2019 with walking videos, so a real local person.	Video from a named place, the road bridge, with the rugby club visible and the council’s bilingual sign.	Yes. D says the footbridge closed at about 17:30.	4	Filmed on the spot and matches the council, but she is not a journalist and it only shows one place.
B: “dam CRACKED”	“Wales News NOW”, no person named, joined 3 weeks ago, 212 followers. Cannot check.	One photo with no date or place. Capital letters and “SHARE before they delete it”.	No. D, E and F all say the dam is safe. F shows the photo is from 2021 in another country.	1	Anonymous, no evidence, and every other source contradicts it. The photo shows a concrete dam; Llyn Derwen is stone.
C: community group	An unnamed member sharing Item B, plus comments. The admin is a named role but not a named person.	“My cousin works for the council”, which is second-hand. The admin gives a checkable fact: 11 houses on Glan yr Afon.	The admin agrees with D about the 11 houses and the rest centre. The member’s fear comes from B.	2	Mixed. The admin’s comment is accurate, but the post itself spreads B further with rumour.
D: news website	Valley Voice Online, a named local newsroom, with a named reporter, Rhodri Evans.	Natural Resources Wales flood warning, a council quotation, the reservoir owner’s inspection at 19:00, a police quotation. Update time shown.	Yes. A, E and F agree.	5	Several official sources, named people, exact times, and it corrected the dam claim openly with an update.
E: TV bulletin	Wales Tonight, a regional TV news programme. Reporter at the scene.	Live pictures, the reporter spoke to the reservoir owner, an interview with a resident.	Yes. D and F agree.	4	Reliable, but it names no official source on screen, and it came 1 hour 25 minutes after Item B.
F: fact-check	Check First Cymru, a fact-checking website that lists its sources.	Reverse image search showing the photo is from 2021, the owner’s statement at 19:05, the flood warning, the D article.	Yes. D and E agree.	5	Shows exactly how it checked, lists its sources so I can check them, and explains who is behind Item B.

(a) The first correction by a news organisation was the 19:15 update to Item D. From 18:05 to 19:15 is 1 hour 10 minutes. By 19:00, before the correction, Item B already had 94,000 views. (The group admin in Item C questioned it earlier, but the admin is not a news organisation.)

(b) D + E + F = 41,000 + 27,600 + 19,300 = 87,900 views. 486,000 ÷ 87,900 = 5.529…, so Item B had 5.5 times as many views as all three truthful items together.

(c) Item B: 21,300 ÷ 486,000 × 100 = 4.4%. Item F: 2,050 ÷ 19,300 × 100 = 10.6%. The fact-check was shared at more than twice the rate of the false post. It still reached far fewer people because of immediacy: it was published at 20:10, 2 hours and 5 minutes after Item B, when the false post already had over 251,000 views. The first version of a story gets the audience; the correction has to catch up.

Feature	Item B: viral post	Item D: news website
Headline or opening words	“BREAKING!!” and capitals: CRACKED, EVACUATED. Exaggerated: “Whole of Cwmderwen”.	“Footbridge closed and 11 homes cleared as river rises”. Exact and calm.
Image or evidence	A dramatic photo of a different dam, with no caption or date.	No image. Evidence from Natural Resources Wales, the council, the owner and the police.
Who is named or quoted	Nobody. “The media” are presented as the enemy.	The reporter, a council spokesperson, the reservoir owner, a police spokesperson.
How it wants you to feel or act	Panic, and share it now: “SHARE before they delete it”.	Stay calm and keep away from the riverbank. “Nobody else needs to leave their home.”

The false claim reached more people because it was built for virality. Item B used capital letters, a frightening photo and the order “SHARE before they delete it”, so people passed it on before they thought about it. Ordinary users did the rest: in Item C one member shared it “to my family group” because it seemed “better safe than sorry”, turning a post from an account with 212 followers into one with 486,000 views. The truth had less immediacy. The news website did not correct the claim until 19:15, 1 hour 10 minutes later, and careful reporting takes time because it has to be checked. By 22:00 the false post had 5.5 times the audience reach of the three corrections together. Misinformation spreads fastest when fear makes users act as publishers.

I understand why the post worried you, but the dam has not cracked. An engineer inspected Llyn Derwen dam at 19:00 and found no damage, and the water is 1.2 metres below the overflow. The photo in the post was taken in another country in 2021. The only homes that have been cleared are the 11 houses on Glan yr Afon next to the river, so your nan does not need to leave.

	Organisation or author	Title or headline	Platform	Time
1	Rhodri Evans, Valley Voice Online	Footbridge closed and 11 homes cleared as river rises in Cwmderwen	Local news website	Published 18:52, updated 19:15
2	Check First Cymru	No, the Llyn Derwen dam has not cracked	Fact-checking website	Published 20:10

• "Llyn Derwen" dam finds pages that use the exact name, not every page about any dam.
• "Llyn Derwen" dam inspection -WalesNewsNOW24 leaves out pages that just repeat the viral post.
• Cwmderwen flood warning Natural Resources Wales goes straight to the official source.
• A reverse image search on the photo shows where and when it first appeared online. If it first appeared years ago, or in another country, it cannot be tonight’s dam.