Let's look at the situation as it is:
Amsterdam:
Delft:
There are several reasons why these canals (grachten) are not fenced:
- Accidents happen, and yet we're talking about accidents. A large percentage of Dutch people know how to swim, and the canals aren't very deep. In Amsterdam, about 15 people die in the canals every year. The main reason: alcohol.
- The sidewalk is always on the far edge, closest to the buildings
- As you can see, there's little space. It's not convenient to walk along the many canals. Where it's more convenient, the sides are often lower or there are steps.
- When cars can park along the water (pictured above) the space is even smaller.
- Fences are often present where there is a real risk of falling. Bridges and other narrow areas or places with heavy traffic have fences.
- Fences must be high enough to effectively prevent accidents.
We Dutch are also used to water.
This is a common sight in more rural areas:
A small road, when the grass is soft there is often a warning sign on the roads:
Accidents involving a car ending up in water are very rare in cities and much more common on country roads. It's best to be sure you can handle your car when parking near water.
Ultimately, it's about risk. There's very little risk of people falling into the canal, especially considering how many people use it every day. People, when they're not drunk, understand the dangers of the water and are unlikely to fall into the canal.