A 13-km (8-mile) waterway

A sweeping vista of the Seine as it makes its entrance into Paris, the beginning of the river’s 13 km (8 miles) journey through the capital. The Seine is France’s second longest river, (776 km long - 481 miles), winding its way from its source near Dijon to finally reach the sea at Le Havre. The Seine is a recognised zone of national ecological importance, a major Parisian blue network asset. The river’s path through the city has been modified by canals since the mid-19th century, and still serves as a natural migration route for various species of fish and birds, as well as plants such as the common alder and yellow flag iris (Iris pseudacorus), whose seeds are spread via the water. The river provides a prime travelling route for many other species of animals in transit.
However, for certain species the Seine represents a serious obstacle: mammals such as the red squirrel and European hedgehog are unable to cross the river, while some fish are unable to get past the dams and locks. If we are to protect and enhance the Seine’s biodiversity, we need to minimise the effects of this fragmentation of different natural spaces. This is one of the objectives of the Paris Biodiversity Action Plan.

A river teeming with fish

The Seine serves as a key migration route for numerous species: over the past ten years 35 species of fish have been observed in the Seine in Paris, up from just 3 in 1970. Of these 35 species, 17 were found to be reproducing in the waters around Paris, particularly in the specially-created spawning grounds.
Things have come a long way since 1970, when the river was almost completely lifeless. The quality of the water has been increasing steadily ever since, with particularly strong progress made since the year 2000. The number of water treatment stations has increased, in addition to their improved efficiency. The region’s industrial infrastructure has evolved and waste products are now partially pre-treated before being released into the general waste water network. Oxygen levels in the Seine have thus increased by 10%, paving the way for numerous species to return.

Every day hundreds of keen anglers set up their rods on the banks of the Seine. One of the most common catches is the silver bream (Blicca bjœrkna), a fish which favours calmer waters and travels in groups. It is, however, still strictly forbidden to eat fish caught in the Seine on account of the dangerous levels of toxins accumulated in their flesh (metals, lead, arsenic, PCBs etc.), reflecting the widespread but invisible micro-pollution of the waters.
The presence of rainbow trout (Oncorhynchus mikiss) and brown trout (Salmo trutta fario) can be attributed to the regular restocking efforts led by local angling clubs, as well as a certain degree of natural reproduction. However this natural reproduction only occurs upstream of Paris, closer to the Seine’s source, where trout thrive in the cooler, more oxygen-rich waters. These trout are among the species which have gradually repopulated the Seine as the river’s water quality has improved. The presence of trout is also a sure sign that the smaller fish and invertebrates which make up their diet have also returned to the Seine. The study currently being conducted on the biodiversity of the river and its banks, with a vision to define and protect the city’s blue network, has identified the brown trout as a  ‘Parisian target species’, as it is considered representative of this freshwater habitat.

Transportation on the river

Upstream of the bridge sits the bustling Port de Tolbiac. Every day thousands of tonnes of building materials and rubble enter and leave the city via the river. Over 20 million tonnes of goods pass through the Ports de Paris every year, keeping over 1 million extra trucks off the streets of the Ile-de-France region (one barge is capable of carrying the equivalent of 250 truck-loads). Taken together, the Ports de Paris represent France’s largest port facility, and the second largest in Europe. From the bridge at Tolbiac you can see the concrete mixers which come here to stock up on sand and cement, keeping Paris’ building sites running. The refurbishment of the concrete plant to meet High Environmental Quality Standards (French HQE certification) shows the port authority’s new environment policy in action, with its commitment to reduce the ports’ greenhouse gas emissions. Every year over 280,000 tonnes of goods pass through the Port de Tolbiac alone, avoiding 14,000 extra truck journeys on the streets of Paris. The use of river transportation also produces 2.5 times less CO2 per tonne transported than the road freight alternative.

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