Africans and Maghrebis have always sought to enter Europe illegally across the Strait of Gibraltar, despite tight military controls of both coastlines in recent years.
But in past weeks the number of espaldas mojadas (wet-backs) hazarding the trip in flimsy inshore fishing boats has risen sharply.
Civil Guardsmen patrolling this 70-mile stretch of Spanish coast have detained 796 illegal immigrants this year, mostly Moroccans, double the figure for last year and for 1993.
If the rate of clandestine crossings continues - and dawn landings are now being reported almost daily - the figure could match that of 1992, when 1,565 people entered Spain illegally through the southern gateways of Tarifa and Algeciras. Corporal Jose Maria Gomez pointed down the jagged cliff, past the ruins of an old barracks, to the spot where one of the pateras (little boats) came to grief earlier this month: "That was where the patera capsized. Two of the illegals died and their bodies washed up a few days later over there. We captured three and at least six ran away and escaped.
"They can hide in the hills until it's dark. People in the area give them clothes and food. And at nightfall they clamber up to the main Algeciras road and make their way up the coast. Poor things," he adds. "They're not delinquents."
The influx of 1992 prompted the Prime Minister, Felipe Gonzalez, to visit King Hassan in Rabat, and each side promised to tighten controls. Since then, Moroccans landing in Spain without visas have been deported within 24 hours. Other nationalities are held in a detention centre in Algeciras for 40 days, and given a month to put their papers in order.
Faced with this impossibly tight time-frame, most slip into Spain's grey economy, where they dodge and duck to escape detection and scrape a living.
Salif, a Senegalese, came over in a boatload of 20 three years ago. "I had to pay 60,000 pesetas [pounds 300] up front to an outfit in Tangier that organised the boat, and I put my name on a list. Then I sat around in Tangier waiting for my turn."
The mafia which organises this lucrative traffic is becoming more active. "They used to just wait for people to approach them in Tangier, but now they are going into the villages recruiting people and promising them a safe passage," says Julio Martinez, president of the immigrant support organisation Welcome to Algeciras.
"Sometimes they just take people's money and drop them a bit further down the Moroccan coast. Sometimes the boats just don't make it."
In the little white-walled cemetery at Tarifa, a common grave that faces Mecca contains the remains of some of those who perished in the attempt. Countless others were washed away without trace.
Salif was lucky: "We set off at dawn, crouched in the bottom of the boat, and the crossing took two hours. We had to swim the last 50 yards and met a welcoming committee of Civil Guardsmen, police and the Red Cross." But he eluded the authorities, and now makes a living selling cheap clothes on the beach.
In explaining the increased traffic, observers point to the drought that has ravaged Moroccan agriculture this year, forcing farm workers north in pursuit of survival.
"They know that they can get work, albeit precarious and badly paid, on plantations in southern Spain around Almeria," says Mr Martinez.
Others believe Morocco may have relaxed its guard on its coast, enabling greater numbers to slip away, a matter on which Spanish authorities remain carefully neutral.
"We have no official confirmation that Rabat has lessened its vigilance," said a spokeswoman for the Andalucian civil governor in Cadiz. Spain is waiting to see if the increase persists beyond the fine summer months.
"It is too soon to say whether this is a permanent trend. We are maintaining our vigilance and we are not alarmed," the spokeswoman said.
The Civil Guard has four patrol boats and a helicopter constantly on alert. But it admits it has no idea how many immigrants slip through.
"They see images of Europe on Spanish television in Morocco and think it is El Dorado. There are lighthouses here in Algeciras and Tarifa. You don't have to be a nautical genius to make the trip," says the Civil Guard's commander-in-chief for Algeciras, Lieutenant-Colonel Mariano Jorge. "Even if we put up a Berlin Wall, people would find a way round it."
Most come in pateras, others are smuggled in fishing boats or cling to the undersides of lorries on the ferry from Tangier or Ceuta. Some picked up at sea are smuggling hashish, Col Jorge says. When spotted, they tip their cargo overboard and declare themselves immigrants, preferring deportation to prison.
At Algeciras port, carloads of Maghrebis pour off the ferry from Tangier, bound - judging from their number-plates - for France, Belgium and Holland, after visiting their families. These are the ones who made it to the promised land and hundreds of thousands of them converge on the Algeciras crossing-point every summer.
More and more Moros, as Spaniards still call them, are trying to cross, before the European frontier surrounding the Schengen group of countries clangs shut. Legal entry into Europe is increasingly difficult. "There has been a 25-per-cent increase in visa requests this year," says Spain's consul in Tangier, Pablo Bravo.
"Those seeking entry to Europe via Spain are experts on Schengen. They know that with a Spanish visa they can go anywhere in Europe. We have to take more precautions, so it's harder for us to grant visas."
With legal avenues closing, pressure mounts on clandestine routes. "It is inevitable," Mr Bravo says. "Even Felipe Gonzalez would take his chance in a rickety little boat if he saw better prospects only 14 km north."