Swimming Against Undercurrents

Undercurrents can be a hazard when diving off shore.
i Comstock/Comstock/Getty Images

When trying to stay safe in the water, many swimmers and divers focus on avoiding hazards such as debris, boats and other swimmers. If you swim or dive in large bodies of open water, however, an undercurrent is a less obvious hazard that can be very dangerous. Understanding what undercurrents are and how to escape them can keep you safe even if you encounter an unexpected undertow.


Undercurrents are currents of water that flow under the surface of a large water body; they are like a small stream or river within the larger water body itself. They are a natural part of the flow of lakes and oceans and are essential to maintaining a balance of heat and nutrients in the water. Often caused by temperature differences that occur in deep water, undercurrents can also be caused by weather; underground rivers or springs that empty into a large body of water; or the flow of water through manmade structures such as dams.

Undercurrent Intensity

There are different types of undercurrents that you may encounter in lakes and in the ocean. Some are slow-moving masses of water that you can feel, but they provide very little resistance to swimming. Faster-moving undercurrents provide more resistance and may be difficult to swim against. Some undercurrents are fast and strong enough that they actively pull you along with them if you encounter them; these are often referred to as riptides or undertow and may be very difficult to break away from if you don't use proper technique.

Dangers of Undercurrents

Basic undercurrents are not necessarily hazardous; but strong undercurrents and riptides can be very dangerous indeed. If you encounter a strong undercurrent, struggling against the current can lead to exhaustion that prevents you from making it back to shore. Being swept up in an undercurrent can result in injuries as a result of rocks and other hazards that the current might flow past. Divers may experience the bends or other dangerous conditions due to changes in body pressure from the speed of the undercurrent. If you aren't diving or don't have an air tank, drowning can be a serious danger as well if the current pulls your head underwater and you are unable to break free.

Recognizing Undercurrents

There are things that you can look for to decrease your likelihood of encountering an undercurrent when swimming or diving. Water with an undercurrent is more likely to be still or have only small waves due to the movement of water under the surface; this is especially evident when larger waves are disturbed by the undercurrent. In some cases you can see undercurrents through the water as well, either as a rippling under the water or as a mass of water that appears to be a slightly different shade than the water around it. You may also see clumps of debris or streaks of mud or sand moving through the water, indicating that an undercurrent is present and is pulling the debris or soil along with it. Undercurrents can vary significantly in size but are typically less than 100 ft. wide.

Swimming Against Undercurrents

If you encounter an undercurrent, it's important that you don't panic. Slow-moving undercurrents may provide increased resistance against your swimming but aren't likely to carry you away. Faster currents will push you under the water but you can escape by swimming parallel to the shore until the current releases you; then swim back to the shore. Very fast currents that pull you forcibly along can be escaped as well: Avoid struggling against the current and either attempt to swim parallel to the shore or lie back and allow the current to carry you until it dissipates, typically 50 to 100 yards from shore. If diving, you may also escape by removing the weight belt that keeps you underwater and inflating your buoyancy compensator. Spread your arms and legs to slow your ascent once you escape from the current to avoid the bends or other conditions caused by rapid ascent.

Avoiding Undercurrents

The best way to keep yourself safe from undercurrents is to make sure that you are prepared in case you encounter one. If you are likely to swim in the open ocean, large lakes or other areas where undercurrents may occur, take a swimming safety class that will teach you proper open water safety techniques and how to escape from undercurrents. Search online or talk to people who are familiar with the area to see if there are reports of undercurrents in the water you plan on swimming in; keep in mind that some undercurrents dissipate over time or vary in intensity based on the seasons or other conditions. Always look at the water before entering it to see if there are any signs of an undercurrent, but remember that not all undercurrents produce signs that are visible from above the water.

the nest