La Gola de Marchamalo in La Manga
A manmade canal between the Mar Menor and the Mediterranean
The 22-kilometre strip of land known as La Manga is punctuated by five “golas” or canals, the southernmost of which is the only one to be entirely manmade and lies near to the main entrance of what is known as “the 
La Manga strip” by tourists and simply La Manga by those who live there. This is the Gola de Marchamalo, and while in the past it was used for the “encañizada” fishing technique, like the other Golas, today its main functions are to allow the water level in the Mar Menor to remain level with that of the Mediterranean and to allow the transit of fish and small boats.
The issue of water level in the Mar Menor is an important one. In times of heavy rainfall it can become swollen and rise above the Mediterranean, and at the same time the shallow water evaporates quickly and causes the high salinity of the water which brings about the migration of some fish species. It is this migration which favoured the development of encañizada fishing through the other Golas during the 
period when the Region of Murcia was under Moorish rule, a period which lasted 500 years from 711 to 1243, although many Moorish inhabitants remained in the area for a further 250 years after Christian forces from Castile y León conquered Murcia. Encañizada is a fishing technique which, to explain it in its most simple terms, involved driving canes (cañas)into the mud to create almost maze-like structures along which fish heading in one direction would swim and then be unable to exit as they hit a dead-end and found themselves trapped.
However, the Gola de Marchamalo dates from over 500 years after the Reconquista of Murcia from the Moors in 1243. In 1762 the licence to build it was granted to the Real Hospital de la Caridad in Cartagena precisely 
so that encañizada structures could be set up here in this channel, close to Cartagena city. When the urban development of La Manga began in the second half of the 20th century, though, fishing activity was quickly curtailed – the last nets were removed in the 1980s - and a permanent bridge was built over the Gola to replace the rickety structure which previously existed.
In the wake of the bridge came the building work which now makes La Manga visible from dozens of kilometres away on the other side of Cartagena, and apart from the large apartment blocks in the area another development was the creation of the first marina, now home to the Club Náutico La Isleta. ( see two old images showing the first development in the area.)
The Gola de Marchamalo is currently so shallow that only canoes and the smallest of boats can pass through, and the fact that it is artificial means that dredging is frequently necessary. The last major dredging took place in 2011. The bridge is also too low for sailboats to use the canal, and as a result there is barely any maritime traffic along the canal.
For many years small boats were moored in the Gola, but the Department of the Environment finally legislated to have them removed in 2011 and they are no longer a feature in the canal.
Click for map, Gola de Marchamalo La Manga