There are two types of mirage visible on Toyama bay: a spring mirage and a winter mirage.
The Spring Mirage
This mirage is particularly famous. It is generally visible from April to June, some years appearing only once or twice, other years several dozens of times. It can appear for a period of anything from a few minutes to several hours. During the shorter periods, the mirage moves closer to sea level. The spring mirage is often visible over the shores of Uozu City.
The Winter Mirage
Although this mirage is often visible all year round, irrespective of season, it is primarily visible in the winter, hence the name. It appears more often than the Spring Mirage and, on a calm day, it will stabilize and be visible for many hours, sometimes even an entire day. This mirage can be seen from anywhere along Toyama Bay and is steadily visible on a clear winter day from any of Himi's shores.
Why mirages appear in Toyama Bay
When there is a large difference between sea and air temperature, the air nearest the sea surface will warm or cool. When the air density suddenly changes in a perpendicular direction, straight-moving sunlight rays will bounce and go off in a completely different direction, turning the view 10 to 40 km away on the opposite shore into a virtual image, or mirage.
To see the mirages, look a little above the sea surface at which point an invisible line will split the real image into two. The image below the line will be a smaller upside down mirror image of the real one above. It is the same phenomenon as the blurry reflection that appears over road surfaces seen from a distance.