Beach near Pisa?

The closest place to dip your toes is the River Arno, which passes through Pisa. However, since by that time the river waters will have passed through Arezzo, Florence, and Pisa (and anything in between) the water will feature excrement from populations of 3 separate provinces. The closest seaside resort town is Marina di Pisa, which is right at the mouth of the Arno on the sea, therefore may not be much better. For the sake of your toes I therefore recommend you either head north, to Viareggio, or south, to Quercianella or Castiglioncello. All of them have excellent train connections with Pisa and their respective stations are a stone throw from the beach (especially Quercianella and Castiglioncello). Marina di Pisa (and Tirrenia, just south of it) is served by buses only.

As always, thanks Roberto, you give great advice! You're right, we'll prefer to wade into places less influenced by waste disposal than the Arno.

Robert

Viareggio is definitely what you want.