Chinese cocklers ignored attempts by fishermen to warn them of the dangers posed by the incoming tide, Preston Crown Court heard.
Fishermen had warned the Chinese of the danger, the court heard
Twenty-three cocklers, all illegal immigrants, drowned off Hest Bank, in Morecambe Bay, last February.
Trevor Fleming, 31, said he and colleagues tried to warn the Chinese cocklers by tapping their watches but were ignored.
Five people are on trial in connection with the deaths of 21 cocklers.
Mr Fleming told the jury he and his colleagues had used quad bikes to drive out to the cockle beds but had been forced to turn back by the bad weather.
They saw several Chinese workers starting out on the 40-minute walk towards the beds, despite them only having one-and-a-half hours before the tide would start to come in.
Mr Fleming said: "I approached one of the Chinese workers. He refused to speak English to me either because he couldn't or because he didn't understand me.
"My friend and I tapped our watches to try and tell them about the time but they ignored us."
John Bromley-Davenport QC, defending Lin Liang Ren, asked if it was sensible for inexperienced people to tackle the sands.
"No, not at all," said Mr Fleming.
'Matter of time'
"Anybody who goes out on the sands is risking their lives.
"It was only a matter of time before there was going to be a tragic accident."
Mr Fleming added that he had warned the coastguard, fisheries department and police about his fears, but said his warnings were ignored.
The cocklers' alleged gangmaster, 29-year-old Lin Liang Ren, from Liverpool, denies 21 counts of manslaughter.
He also denies a charge of perverting the course of justice and an immigration offence.
His 20-year-old girlfriend, Zhao Xiao Qing, from Liverpool, denies perverting the course of justice and an immigration offence.
Lin Nu Yong, 31, also from Liverpool, and father and son David Anthony Eden snr, 62, from Irby and David Anthony Eden jnr, 34, from Prenton, both in Merseyside, also deny an immigration offence.