ABOVE: Before cooling your heels in Venice's canals, put on latex socks.

In the summer months, it isn't uncommon to see tourists dipping their toes or feet into Venice's canals, presumably in an effort to keep cool.

Before emulating those clueless or intrepid visitors, consider this: An estimated 90 percent of Venice's human waste is flushed directly into the city's canals, and a public-health study detected Hepatitis A virus and enteroviruses in 78 percent of the canals that were tested over a two-year period from 2003 to 2005.

Venice's canal-based sewer system is more than a thousand years old, and it continues to work well by medieval or pre-Victorian standards.

The principle is simple: Venice's canals are flushed by tides twice a day, and the receding tides pull waste from the canals into the Venetian Lagoon and ultimately toward the Adriatic Sea. As a bonus, saltwater has a mild sanitizing effect. (Dilution helps, too--there's far water in a Venice canal than in a typical sewer pipe.)

Critics point out that detergents and other modern "grey water" pollutants interfere with the natural breakdown of fecal matter. That may be true, but even if it weren't, the fact remains that dumping raw sewage into public waterways isn't acceptable in the 21st Century.

The city has made some efforts on the sewerage front--renovated properties are theoretically required to have pozzi neri or septic tanks, for example--but for the most part, building drains flush directly into the canals, and the gospel song Wade in the Water is bad advice for visitors to Venice.

 More photos:

ABOVE: A visitor enjoys a fecal footbath. 

ABOVE: During acqua alta (tidal flooding), water from Venice's polluted canals oozes into the streets.

ABOVE: A pozzo nero ("black well") boat sucks out a septic tank at a bar near the Campo San Giacomo dall'Orio.

ABOVE: A bicyclist poses as a passerby takes his photo on a footbridge.

Back in 2010, we wrote a Stupid Tourist Tricks post titled "Bicycling in Venice" that showed visitors taking two-wheelers into Venice's historic center. Bicycling in the city center was illegal then, and it still is--although you might never guess it from the number of clueless or rebellious tourists who can be seen with bikes near Venice's railroad station and Piazzale Roma.

To be fair, the prohibition against bicycles may not be obvious to visitors who haven't done their research, and not all offenders are tourists. (A few years ago, we often saw a local man arrive by bicycle at his workplace near the Campo Santa Margherita in Venice's Dorsoduro district.) 

A suggestion to Venice's authorities: Place "No bicycles allowed in Venice" signs near the exits from the Piazzale Roma and the Santa Lucia Railroad Station, and make it more obvious where visitors can park their bikes. That way, bicyclists wouldn't have an excuse for bringing their biciclette into the city center.

More photos:

ABOVE: A pair of bicyclists enter Venice's Santa Lucia Railroad Station from the pedestrian zone.

ABOVE: Another bicycling couple roll their bikes across the Calatrava Bridge between the railroad station and the Piazzale Roma.

ABOVE: A visitor hauls his bike over the Scalzi Bridge near the railroad station.

ABOVE: A man explores the city center on what appears to be a folding unicycle with training wheels.