Great Barrier Reef - Human Impacts

Population pressure
Increased population pressures on mainland North Queensland have resulted in increased levels of pollution and physical activities related to tourism on the reef area. 

Tourism
The outstanding beauty of the reef attracts millions of tourists each year. The pressure placed on the reef as a result of tourism includes developments on the shoreline (and associated sewage, rubbish) increase boating activity (including oil spills, coral breakage as a result of boat propellers), and tourist activities (breaking corals while snorkelling, walking on reefs, accessing sensitive areas).

Agriculture (particularly Sugar cane farming)
Agriculture, especially sugar cane farming on the mainland, has resulted in increased sediment and fertiliser run-off from cane farms. In recent years, a downturn in global prices for sugar cane has resulted in farmers using greater amounts of chemicals. These chemicals run off into coastal streams and result in algal blooms and eutrophication in some areas of fringing coral near the mainland.

Sugar cane farmers apply fertilisers containing Nitrogen (N) and Phosphorous (P). Many put on extra fertiliser in case of heavy rain (so it is not all washed away). The introduction of bananas as a crop in the area further increased the use of fertilisers. Of all fertilisers applied, only a third is absorbed by the crops. The rest is either evaporated, enters groundwater or runs off into nearby rivers or canals. Sugar cane crops need water to be drained away quickly. If the crops are left in water the roots will rot. As a result canals were built to drain water away quickly from the crops in case of heavy rain. These canals, or drains, reverse the cycle of how wetlands are meant to function. Rather than regulate and slow the flow of water, the water is quickly moved away from the site and into main river systems. The water rushes off the land carry fertiliser, soil, pesticides, etc. Actually pinpointing the sources of sediment is difficult, but it is believed that most is coming from land which has been tilled and let lie fallow. Sediment is also coming from bank erosion. Since European settlement erosion has accelerated due to clearing of land (less tree to stabilise soil). Due to erosion the river can erode into paddocks. There is believed to be four times more sediment reaching the coast than prior to European settlement, and in some places it is closer to 40 times. 

Fishing
Recreational and commercial fishing have had major impacts on the reef. Commercial prawn fishing accounts of a large proportion of Queensland's Fisheries output. Approximately 6 million kgs of prawns area harvested in a good year. Recreational fishing in the General Use zones of the Great Barrier Reef Marine Park (GBRMP) accounts for 75% of the fin fish taken from the reef each year. Commercial fishing includes fishing for crayfish, finfish, reef fish, barramundi and tuna.

An examination of one net which washed ashore showed it contained 14 turtles, a shark and a dugong.

Gamefishing has long been an important industry in North Queensland. 

Pisciculture is a trend involving raising fish in fish farms (e.g. tiger prawns and barrmundi).

Dredging
Dredging is removing sediment from the bottom of a river bed, harbour, etc and placing it elsewhere.
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Links:
Abbot Point: Dredging dumping permitted within Great Barrier Reef waters

Abbot Point approval: Tour operators disappointed by Great Barrier Reef dredge spoil decision
Approval of Galilee mega mine leaves Reef strategy in tatters.

Landuse impacts on Great Barrier Reef water quality and ecosystem condition

Dredging set to swamp decades of Great Barrier Reef protection

WWF - Queensland resources sector needs leadership