Workers in Hangzhou's Sanbao ship lock are busy clearing vessels in preparation for the full impact of the tide of Qiantang River.

The magnificent tide arrived last Friday, the 16th day of the seventh lunar month. At 1:15pm, it reached a high of 0.6 meters but before dawn the following day it rose to 0.8 meters. The tide was predicted to rise still higher in the ensuing days, reaching up to levels of between 1 meter and 1.2 meters during the day time.

According to experts from Hangzhou Hydrological Monitoring Station, the seventh and eighth lunar month of this year - September and October - will be among the best watching periods for the tide over the past six years.

Visitors to Hangzhou can watch three types of tides: crossing tide, one-line tide and undertow.

Two tides join each other in a place named Daquekou (big gap), forming crossing tides. Then they surge up along the Qiantang River and reach the climax near Haining Town.

At that point the swells will shape a long and magnificent wave line. This one-line tide is a major attraction of the Qiantang River tide.

When the waves later arrive at a place named Laoyancang, they surge ahead and hit a 660-meter dam wall, resulting in huge undertows. A second undertow can be seen at the Beauty Dam of Xiaoshan City.

Wonderful as the waves are, when, where and how to watch them are worthy of careful study. The surges might turn into threats to visitors' security.

Normally the tide will reach 1 to 2 meters, sometimes even 3 meters. The powerful reaction of the water hitting the dam wall can lift the waves higher than 10 meters. They surge at an average speed of 20 kilometers per hour and a maximum of 10 meters per second.

That means a person has to run faster than Usain Bolt to flee the tidewater. The pressure of the waves is up to 7 tons per square meter.

Influenced by variables such as climate, geography, astronomy and hydrology, the Qiantang River tide is subject to frequent changes. The perfect watching spot often becomes a dangerous one.

Seen from afar, some waves seem quite smooth but can escalate to uncontrollable billowing the minute they hit. Hence, swimming in the Qiantang River is highly risky.

Six most dangerous watching spots:

Daquekou

It is located near the sea where the tide starts. The distinctive landform of Daquekou inside the Xiaojian Mountain helps form the powerful crossing tide, making it the first dangerous spot.

Laoyancang

The crossing tide surges ahead to make the one-line tide near Yanguan City. Then the waves hit the dam wall in Laoyancang, forming strong undertows.

Beauty Dam

Two dangerous spots are located at the Beauty Dam because of the undertows.

Qige Village

The Qiantang River has another turn at Qige, making it a risky spot.

Qibao

Undertows often appear near the Qibao Hydrology Station because of a T-shaped dam there. However, many people often swim in the river or stay on the dam, hence many accidents happen here.

Also be careful at other watching spots and remember not to climb over the dam.