Marine scientists say sewage and 'nutrification' – the effects of excessive nutrients – reaching marine systems are among the four most serious problems for the oceans associated with land-based activities. In January 2001 the UN experts declared:
"At the global level, the most serious problems associated with land-based activities are:
- sewage;
- the physical alteration and destruction of habitat;
- excessive nutrient inputs; and
- sediment mobilization."
Source: GESAMP71:4
GESAMP (IMO/FAO/UNESCO-IOC/WMO/WHO/IAEA/ UN/UNEP Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection). 2001. Protecting the oceans from land-based activities - Land-based sources and activities affecting the quality and uses of the marine, coastal and associated freshwater environment. Rep. Stud. GESAMP No. 71, 162 pp. ISBN 82-7701-011-7.