Although it has a great body of water, the impetuosity of the current, rushing amongst rocks, forms dangerous rapids.
The surface of the lake must be considerably above the sea-level.
The approaches to the northern end of the lake on both sides of the river were defended by many cottas, or forts. Most of those were taken and destroyed by the Spanish forces in 1894–96, but they are now probably being rebuilt.
Half-way between the lake and the Bay of Iligan stands Fort Weyler, which had a strong garrison of infantry, cavalry, artillery and engineers, and was impregnable to any Moro attack. To the south of the lake, on the shores of Illana Bay, stand Forts Corcuera and Baras, whilst to the westward, between Illana Bay and Panguil Bay, lie four forts across the narrow isthmus called Alfonso XIII., Infanta Isabel, Santas Paz, and Eulalia and Maria Cristina.
These, with the trocha, or military road of Tucúran, cut off the Illano Moros from communication with their brethren of Sibuguey, or with their former victims, the Subanos.
Further to the northward, Fort Almonte kept watch over the quondam pirates of the Liangan River.
These forts and posts were garrisoned by nearly 3000 regular troops, all natives, except the artillery (see List of Posts in Mindanao, p. 386), and in addition a field force of several thousand men, also of the regular army, was encamped at Ulama, Pantar, and other places to the north of the lake, and three small steam-vessels had been transported overland in sections, and launched upon the lake.
Thus everything was ready for the final blow, for the Moros were completely hemmed in by Spanish garrisons or Jesuit reducciones; but the breaking out of the Tagal insurrection, in 1896, obliged General Blanco to withdraw, not only the field army, but to reduce the garrisons in order to hold Manila and Cavite until the Peninsular troops could arrive.
Later on, the war between the United States and Spain, and the immediate destruction of the Spanish naval forces by the American squadron, caused the Spanish authorities to sink the flotilla in the lake, to abandon all the posts on the north coast of Mindanao, the trocha of Tucúran, and all the forts on the Rio Grande, and to concentrate their whole force at Zamboanga, leaving the recently-converted heathen and the missionaries to defend themselves against the Moros as best they could.
The missionaries of the district of Cotta-bato have taken refuge in Zamboanga, fearing to fall into the hands of the Moros, who would exact a heavy ransom for their delivery. As for the hundreds of liberated slave children, both girls and boys, who were gathered together under the protection of the missionaries at the asylum of Tamontaca, they are doubtless once more in the hands of the cruel Moros of Lake Lanao; some, perhaps, have been sold by these wretches to the heathen tribes for twenty or thirty dollars each, to be offered up as sacrifices to Tag-busan, the god of war of the Manobos, or to Dewata, the sanguinary house-god of the Guiangas.