This can be a major problem. Such is the demand for building land right along the Andalucian coast, that developers would rather construct apartment blocks than use available land for boat storage. A number of companies have got around this by leasing out space to owners in 'naves', or warehouses which are set back from the coast in less desirable building land.
However, the majority of owners usually let their boats lie in the water right throughout the year, unless work is required to be carried out. The temperate climate of southern Spain means that boats are rarely in danger of suffering physical damage, so it is less of a risk to leave a boat in the water all year round.