Over roughly a month, the jokers constructed the three saucers in Dave Maloney's shed using old communication dishes, some lights and a bit of ingenuity.

Then they dragged them out into a paddock by the Hopkins River on Wednesday at dusk, fired up the generator and sat back and watched as dozens of onlookers stopped to check out what looked like a scene from a sci-fi movie.

"There's been quite a few cars slow down and people taking photos," Mr Maloney said.

"A few mates rang up to tell me I'm an idiot."

The two bigger saucers measure about three metres in diameter and the smaller one is about 2.4 metres in diameter.

"They're made out of aluminium and fibreglass and they take four blokes to move them," Mr Maloney said.

He said the idea "probably came out of a bottle" and that making the non-flying saucers had been a good time-filler "instead of watching TV".

"I just like doing pranks and stupid things now and again. You've got to have a bit of fun."

The only downer was that some idiots had done doughies and burn-outs around the saucers early Thursday morning, he said.

"I'm spewing about the burn-out marks around them 'cause they looked really good sitting there in a nice green paddock."

Warrnambool radio stations also broadcast the news of the UFOs, including information about the "landing site" being investigated.

The other big April Fools' Day joke of the day came from Flagstaff Hill manager Peter Abbott, who sucked in quite a few people with his big announcement on ABC Radio that US President Barack Obama would be visiting the maritime museum with his family during his Australian tour in June.

Mr Abbott sold the story beautifully by linking a web of connections.

The new American ambassador to Australia is from San Francisco, which is where the American whale boat crews that competed in Warrnambool recently were from, and Mr Abbott explained that the ambassador's nephew was among the whale boaters.

After the nephew talked up Flagstaff Hill to the ambassador, and with Prime Minister Kevin Rudd visiting there recently, word filtered through to the Obama camp.

And as Mr Abbott was in the US last week "visiting security officials", the story fell into place perfectly.

"It all tied together so nicely I almost started believing it myself," Mr Abbott laughed.

With a bit of help from ABC Warrnambool, there was even a number people could ring to go in the ballot to join Mr Obama for a special Shipwrecked Show. Dozens got on the phone.