Reading Open-Water Currents: Use the Flow When Swimming With It, Stay Alive When Swimming Against It

Introduction

Many open-water swimmers notice something strange during training or races: even though they are swimming the same route as usual, today it feels especially strenuous, and they keep drifting off course. This is often not a fitness issue but the work of water currents. Currents are one of the most unpredictable factors in open water, but once you master the basic methods of reading them, you can turn passivity into initiative and swim safely and efficiently in all kinds of water.

Current Characteristics of Taiwan’s Major Open-Water Areas

Sun Moon Lake (lake current):
Sun Moon Lake is an alpine lake, mainly influenced by its inlet (water flowing in from the Zhuoshui River source) and outlet (pumping by the Sun Moon Lake hydroelectric plant). The flow direction is not fixed, and the speed is relatively slow (usually no more than 0.3 m/s). However, in strong wind conditions, noticeable surface wind-driven currents may appear on the water, interfering with swimmers’ sense of direction.

Taitung Living Lake (circulating current):
Living Lake is a man-made training lake. The water flow is controlled by an artificial circulation system with a stable speed, making it an ideal venue for practicing swimming techniques in currents.

Penghu waters (tidal current):
The Penghu Strait is one of Taiwan’s strongest open-water current areas. During flood and ebb tides, the current speed can reach 1–2 m/s. If you do not understand the tide times, swimming against the current may make progress nearly impossible.

Kenting Bay (longshore current and rip current):
Kenting’s coastline features complex longshore currents and seasonal ocean currents. When the northeast monsoon weakens in summer, rip currents occasionally appear near the Daren area, making it a higher-risk zone.

Basic Types of Currents

How to Read Current Direction?

Visual reading before entering the water:

• Observe the movement direction of floating objects on the surface (leaves, foam lines) for a preliminary indication of surface current direction.
• Watch for obvious “flow lines” on the water surface—there are often subtle streaks or color differences along the direction of the current.
• Observe other swimmers already in the water near the shore, and note whether their bodies are being pushed off course when they swim in a straight line.
• In areas with currents, small eddies form behind fixed objects (buoys, moored boats), which can help determine flow direction.

Sensing current direction in the water:

• While swimming, if your body keeps being pushed to one side, it means there is a lateral current. You need to actively correct your heading (when fighting a cross-current, aim upstream of your target point).
• If your strokes feel labored and your speed is unusually slow, you are likely swimming against the current; if it feels easy and fast, you are likely with the current.

Strategies for Swimming With and Against the Current

Swimming with the current:
A following current can significantly boost your speed and serves as a “natural assist” you can use. When planning a training route, if you have the choice, make the return leg go with the current. Note: when speed feels easy, do not relax on navigation, because the current can carry you off course.

Swimming against the current:
Do not stubbornly fight a strong current. Instead, lower your pace appropriately and use a technique of “fuller strokes each time” to reduce wasted energy. If the opposing current is too strong (>1 m/s), assess whether you can take a detour to avoid it rather than confronting it head-on.

Rip current self-rescue:
If you accidentally enter a rip current:

1. Do not try to swim directly back to shore (you will exhaust yourself).
2. Swim laterally to escape the narrow band of the rip current (usually no wider than 30–50 meters).
3. Once clear, swim diagonally back toward shore.
4. If your strength is insufficient, float and call loudly for help while waiting for rescue.

Practical Advice

• Before swimming in Penghu, always check the day’s tide times (the Central Weather Bureau website provides tide forecasts for all of Taiwan), and choose to swim around slack tide (tide transition) when the current is gentlest.
• During training, deliberately choose sessions under different current conditions and consciously practice maintaining a straight line in cross-currents and opposing currents.
• Talk with locals or coaches familiar with the venue to learn the site-specific current patterns—this is far more efficient than figuring things out on your own.

Conclusion

Reading currents is the skill in open-water swimming that most requires accumulated experience. From visual observation to in-water sensing, every time you enter the water is an opportunity to understand currents. Turn currents from a “threat” into a “tool,” and your open-water swimming will reach an entirely new level.

Related Reading

• Reading Currents in Open Water: How to Use Sea or River Flow Direction to Save Effort
• Reading Tides and Ocean Currents: How to Use Water Flow to Conserve Energy
• Open-Water Swimming Safety Rules: Buddy System, Current Reading, and Emergency Response
• Open-Water Swimming Safety Guide: Dealing with Tides, Water Temperature, and Visibility