The maximum tidal range in the Algarve is just over three metres (for free tidal predictions go to The Uk Hydrographic Office); this leads many people to make the mistake of expecting lateral movement of water as a result of tide. But they are wrong. The problem occurs for visitors to the Algarve who learnt to sail or motor cruise in northern Europe. They are used to tidal streams and to allowing for them in their navigation. We have tidal streams in the English Channel, the North Sea and the Irish Sea because they are narrow, funnel-shaped channels that water moves rapidly up and down with the ebb and flood of each tide. But here in the Algarve we have the entire Atlantic before us. There are no narrow channels and so the water just changes depth with each tide.

There are, however, strong movements of water at the entrances to the Algarve rivers and harbours. This is particularly noticeable at the entrance to Ria Formosa at Cabo de Santa Maria, where I once experienced a current of eight knots in the middle of a spring ebb. On this occasion I was in a 38-foot yacht and was only just able to get through the entrance under maximum revs by keeping over to the extreme western side. The River Guadiana also has a very strong ebb tide particularly when combined with a strong river stream following heavy rainfall.

Whilst there is no lateral movement of water along the Algarve coast as a result of tide, there are other currents. A warm current (the Gulf Stream) originates thousands of miles away in the Caribbean and crosses the Atlantic in a north easterly direction, making it possible for palm trees to survive in Cornwall. On reaching the approaches to the English Channel some of it turns south and makes a clockwise circuit of the Bay of Biscay, giving a constant west going current of about half a knot along the north coast of Spain. On reaching Finisterre the current turns south and travels at a steady half a knot down to Cabo de Sao Vicente where it turns east and runs along the Algarve coast at half a knot to Cabo de Santa Maria. Here it accelerates to a knot and continues at that rate until it reaches the Strait of Gibraltar where it increases in speed to as much as three knots as it passes through the Strait and into the Mediterranean.

But if there is a wind from the north east through to the south east, this current can actually turn and run in the opposite direction, giving us a west going current along the Algarve coast of up to a knot. This west going current only exists for up to about twenty miles offshore, further offshore the current still runs in a south easterly direction, creating a giant anticlockwise eddy when we have an easterly wind.

Ancient secrets

You may well ask, what happens to all the water that flows so quickly through the Strait of Gibraltar?  The answer to that is that there is more water lost through evaporation in the Mediterranean than is replaced by water flowing in from various rivers. The water level in the Mediterranean is therefore slightly lower than the Atlantic and so water constantly flows in from the Atlantic to top up the Mediterranean. This is why the Mediterranean is saltier than the Atlantic.

There is virtually no tidal effect in the Mediterranean, but the current that I have explained above does flow very slowly round the Mediterranean in a clockwise direction. The speed of this current is so insignificant that it is not worth calculating when navigating.

Some of this current having completed a circuit round the Mediterranean then goes back out into the Atlantic more than two hundred metres below the surface of The Strait of Gibraltar.  Phoenician traders (1200 to 300 BC) are said to have used this west going current in order to pull their ships westwards through the Strait into the prevailing westerly wind. They achieved this by lowering their square sails on ropes, having weighted them with rocks, more than 200 metres below the surface and were then towed through the Strait by this counter current. When I first heard of this I argued that surely this water having travelled slowly round the Mediterranean would now be much warmer and if anything would want to travel out of through the Strait on the surface, but was told that it would now be saltier and would therefore sink to a lower level than the east going current.

It is my theory that the warmer saltier water that we experience in the Algarve when we have an easterly wind is that same current that has been warmed by its circuit of the Mediterranean.  This reaches our coast via the Strait of Gibraltar then mixes with the colder Atlantic water and is brought to us by the wind-driven, west-going coastal current.